Had the same question myself

not sure Weber would "screw over" his old team without warning... so they could potentially work something out

Isn't it a win-win for Montreal here. League approved trade so blow-back.
The Habs place Weber on LTIR and if he's able to come back for the playoffs then he plays with no cap issues ala Kucherov.
If after the year layoff he decides to retire since he can no longer play to the standards he is used too, then Nashville eats the recapture penalty. If Nashville wants to trade for him during that time so they can buy him out, there should be a piece going back the other way I would think.

I think if it’s injury related, the penalty won’t apply.
So it may be moot.

the situation sucks because i love Weber, but he aged about 3 years this year after looking very good last year and in the bubble...the 7.8M in cap space is a welcomed addition

Not likely. The Habs don't get to control if Weber retires or goes on LTIR. That's up to Weber and the NHL/NHLPA.

The only way it would makes sense for Nashville to trade for Weber is Montreal decides he's going to be a healthy scratch going forward and that might push him to retire early. In that case Nashville could trade for him to keep him active, but that's not worth doing for a few more years, since they'd be taking on his $7.8M cap hit and right now the recapture is cheaper. In the last couple years of his contract that changes.

Montreal is the one that's feeling the pain right now, especially if it's not clear if Weber will miss part of the season, the whole season or retire. Dramatically changes what they can do with that cap space.

If Weber is has knee, ankle, foot and thumb injuries that require surgery, maybe not the thumb. The NHL/NHLPA don't have any say if he goes on LTIR specially if he elects to have those surgeries at a later date.
Reports all over that he won't play next season, never mind healthy scratch, so that's $ 7,857,143 of cap space the Habs will be able to use.

Posted elsewhere but here's an abridged version:

If Weber wants to retire there isn't a thing either team can do so Nashville isn't going to trade you anything to put Weber on LTIR. If Weber is too injured to play and wants to continue being paid, Montreal can put him on LTIR or buy him out (hint... buying him out is harder on Montreal then it is Nashville)