It's unlikely that they'll join Russia, at least in the short term. The 1991 referendum formed the legal basis of the Crimean decision and for whatever international law is worth was legal since all the i's were dotted and t's crossed in terms of Ukraine approving it. Legally, Crimea left Ukraine then. Which is, of course, why it never gets mentioned in the media and they like to pretend that the only referendum was the 2014 one as they can legitimately complain about that one. What exactly the media think the 1992 constitution was that was referenced in the 2014 referendum and how/ why that option meant independence from Ukraine without referencing the 1991 referendum, who knows?
Lugansk and Donetsk are at this point equivalent to South Ossetia and Abkhazia, intended primarily as leverage* in that they can ask to join Russia and be approved, but haven't. If they joined Russia it would be irreversible, as it stands it's still eminently reversible. Russia would probably still be happy with Minsk being implemented, but...
Fundamentally the problem is that Minsk was signed when Ukraine was losing badly, and froze the conflict before it was decided outright. Of course Russia got most of what it wanted in those circumstances, since they could have just taken what they wanted. Now, Ukraine has had 8 years of being told how much better its armed forces are and how they'll get support from US/ UK/ Poland and Russia will have its economy destroyed if the conflict resumes; and domestically 8 years of being told how unfair Minsk is and how it was made at gunpoint. Any pressure from France and Germany to get it implemented is cancelled out by the support from others for it not being implemented. The only way it gets implemented is if there's enough pressure, and if there's a difference between the pressure required for outright war or pressure required for implementation it's very fine. From Russia's pov recognising independence gives Russia the benefits of Minsk without having to implement their side and increases pressure on Ukraine to fold on other issues. It's also gives a lot of difficulty to the west in terms of response; the hawk side will want a robust response** that promotes escalation (or to be more charitable, a desire to show strength in the supposed belief that it will de-escalate, somehow), the dove side will want a weaker response that leaves diplomacy open.
*it's also unclear if the recognition is for the full oblast or just controlled areas. About half of each is controlled by Ukraine. That decision obviously provides further potential leverage
**ironically, that's generally had a detrimental effect on Ukraine despite supposedly being supportive, which is why Zelensky has repeatedly tried to get the rhetoric turned down. It's all very well the US and UK shouting from the sidelines, it's not going to cost them anything being inflexible and inflammatory.