Well, Ukraine joining NATO before removing Russia from its territory is not going to happen[1], and so long as Russia is unable to at least properly shore up/rationalise its 'gains' I can't see a functioning Ukrainian government not biting back at every opportunity, right up to the proper border if at all possible, for at least the rest of the year.
Maybe for several years, but I won't predict a Forever War as, apart from the difficulties of maintaining a Hot Stalemate for that long, some unforeseen/unforeseeable rebalancing is surely going to happen out of the blue. Whether from internal (for either side) elections or other necessary leadership changes, third parties adding more than the current weight of support or world events (natural or political) shifting the whole axis of international focus around. (You can imagine all kinds of things, most improbable but not at all impossible.)
I'm with you in that not supplying arms to Ukraine is one of the worst options for 'the rest of the West' to do. The easiest way to restore peace is for Russians[2] to go home, but the events that lead to that also require events outwith the direct and clear control of Ukraine. If anything, though, that is the outcome that Putin probably fears most, and probably fuels at least some of his paranoia. Fighting NATO-by-proxy is probably the best he could hope for. Which isn't saying much, but of the viable alternatives...
The main point (that I started with) also complicates the Moldova/Transnistria issue, for direct NATO interference, but doesn't prevent (maybe even lubricates) the possible transfer of materielle and the means of training. Pour discourages la Putin, as it were.
[1] It was already off the table whilst they had Crimea and the 'rebel'/Russian-occupied bits of Donbas hanging over their heads. Possibly if they had officially relinquished their natural claims and things had settled down without the diplomatic-landgrab sparking further brinksmanship and border-pushing, for a few peaceful years, they would have been ellegible to properly apply, but it wasn't really a danger (putting the lie to Putin's 'fears') and it did not take a(n attempted) full invasion to keep it off the table.
[2] Russians from Russia, I mean, but I trust that (apart from outright collaborators within the last 8-or-so years of Russian interference, but especially any that tried to facilitate the invasion itself) ethnic-Russians-in-Ukraine[3] won't be overly prevented from returning to their Ukrainian homes at a similar rate as their ethnic-Ukrainian neighbours. Requiring only rebuilding and reconstruction, as necessary, in the post-recovery phase of any of those areas destroyed by the Moscow-led cousins.
[3] A fuzzy distinction as that might be...