Hypothetically, if Russia was willing to negotiate, then yes.
But there are some problems.
First, Ukraine would want another country to guarantee their security. It isn't enough that Russia promises to not attack any further. They could just conduct a false flag operation in a few years and break the peace deal, and nobody would do anything. So for a negotiated peace deal like the one you are proposing, Ukraine would want a 3rd party (The US for example) to promise to defend Ukraine if Russia were to break the deal.
Second, even if it were in Ukraine's best interest, the people might not necessarily agree. If the general public wants Ukraine to keep fighting, then it would be very hard for the government to surrender land without much of a fight.
Third, Ukraine didn't know what the future has in store. They could've seen Russia withdrawing from the north and thought Russia was weak and they could hold the Donbas. Maybe they thought the west would provide massive support. Not just a handful of MLRS for example, but dozens.
And of course, the fourth major issue, is assuming Russia only wants the Donbas. It appears Russia wants a lot more than just the Donbas. They likely want Odessa, Mykolaiv, Kherson, Zaporizhzhia, Donetsk, and Luhansk. They already have most of that aside from Odessa and Mykolaiv. Would Russia be willing to negotiate peace just for Donbas, giving up the rest of the land they've already taken? Unlikely...
Well, he said the marines. Ukraine only has 6000 marines according to wikipedia. They lost a lot in Mariupol, and likely a lot in Severodonetsk, so 80% isn't that unbelievable. But it's impossible to know anything for sure as the government is obviously not going to give out that kind of info.