Presumably there would be no 'submarine holiday' for the RN under this scenario and something like Astute would emerge earlier and in larger number.
Had the threat lasted into 1995, then arguably more Type 23 would be forthcoming at least in planning. With possibly the last ships being of the stretched type, mostly just to ease operational use and maintenance. This might induce government to sell off early build Type 23s rather than cut production.
There was no "threat" in 1990, when the USSR fully existed, and there wouldn't be for the foreseeable future.
All those defense cuts (frigate/destroyer cuts, submarine force cuts, Astute development) were done as a result of things that occurred in 1989, not 1991. Nothing would change even if the USSR existed today because the USSR stopped existing as a threat when Germany decided to reunify. Even if the USSR had never collapsed, I still don't see them producing anymore than a few dozen T-50s and 100-200 T-14s though, but that's more than Russia will likely build.
The entire Cold War was a question over what to do over Germany after WW2 and the Soviets and French wanted to dismember it forever into little tiny countries like German Confederation (charitable, I doubt they would be politically unified), while the British and Americans wanted to rebuild it as a democratic country, and the British and American view eventually won. That question was raised again in 1989 when the DDR began its road to being dissolved and finished in 1990 when Kohl reunified Germany.
There would be zero impetus to spend on more submarines or whatever, because the Cold War had long been over in 1991, and the need for offensive submarine operations into the Arctic Ocean was long gone.
Both Britain and America genuinely had more anxiety over German and Japanese industry in 1990 than they did over the Red Army. The USSR would have withdrawn its Western Group of Forces the same the Russians did in 1994 with no questions asked. That's not what a "threat" does.
With both the A-6F and A-12 dead, I think that's where the F-14D+ can sneak in and stick around.
That was the case IOTL, too, and the Hornet lobby prevailed. The continued threat of AV-MF Backfire divisions provides some additional impetus to the F-14D in this case, but that Hornet lobby is strong.
None of this would happen except Hornet getting bought I suppose.
No super F-14 Tomcat 21s or whatever would exist. None of the attack aircraft like F-35 would have any major diversion from normal, because the Cold War was long over, and there's zero impetus to work on them, and because their bottlenecks are related to being ambitious and highly advanced weapons systems that require decades of development as a rule, rather than any sort of moral component. There might be an extra Seawolf or two, but that had more to do with GDEB's crummy worker management and welders' strike than anything, and Clinton would nuke any additional boats. While I could see Bush Sr. keeping like two or three in the budget items they would probably be killed before being laid down if they could get away with it. So NSSN still goes ahead and produces the 774s. Also no Aegis conversions of legacy surface ships either beyond NTU because the air-missile threat was completely gone, and the CGNs still get canned.
The Soviets killed their Backfire force long before they dissolved, this is well known, and the AV-MF attempted to sue Tupolev for it due to breach of contract, but as defense companies are powerful in the East, as in the West this never happened to any significant degree. By August 1991 the readiness rates were somewhere around 30-40% on average and this was close to typical for the AV-MF through the Backfire's life. They probably would have cut the number of regiments in half to bolster the readiness rates up to mediocre 2020s USAF levels, and overall retreat to the Polish-Soviet border where they'd build a giant wall or something. This would not go unnoticed and people would take it as a sign that the USSR was giving up the (invented) trans-Atlantic interdiction idea at least.
The USA would still grapple with its problems of having no defined enemy that it grappled with in the 1990's, and I guess the big economic crunch of the USSR happens in the early 2000s instead of the late 1990s.
There might be a literal few dozen minor changes that don't matter, such as 50 Notas in existence in a single armor battalion. Maybe a single Yak-44 prototype would exist at a museum, probably not in flying condition. Yak-141 still gets slayed by budget cuts. Ka-50 still too expensive and pilot overload too high to justify mass production, Mi-28 is produced instead, maybe the same number of units but production starts somewhat sooner and gets rockier. Ulyanovsk might be 70-80% instead of half and gets sold to China later on. Second unit is either never laid down, or scrapped like the real life one. Tu-160s probably aren't scrapped in Ukraine, the entire force might be centralized in the Urals or something.
None of these are dramatic changes that result in major trend lines shifting though. Because the USSR blowing up in 1995 and not 1991 is not a major dramatic change. It's probably what people were outright expecting, if you read some of the minutes of discussions from Congress in 1990-1991, regarding future defense programs. Perhaps the Soviet dissolution was less shocking in its violence and more shocking in its relative rapidity but I guess that shows how far cynicism had penetrated the Soviet mindset at the time.
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