Best case, European leaders decide to put the $300B in frozen Russian central bank assets into an escrow account, commit to paying enough out of that every year to match what the US had been providing - so Ukraine and Europe in general can tell Trump, thanks for all the help from the US* in the past, we'd prefer you continue, but no matter what the US decides, we can continue this for at least another year - and remember that we're more likely to use this money to build our own - and Ukraine's - military-industrial capacity than buy in the US.
*even though delivery was too slow and much of it was second or third line so handing it to Ukraine saved you the cost of storage and eventual disposal.