Does disbanding a unit (not a squad) delete it from the game?
If yes, do you get something for it (a worker, some salvaged metal?)

it depends after how many ticks ur disbanding
If ur disbanding after the training is over u will get NOTHING
But if ur disbanding while the training u will get metal & oil ( if u have recruited damage or range or then oil if only armor then only metal)
I'm not that sure but if disbanding the same tick ur recruiting u will get more resources refunded compared to when u do it at last tick of training
Need someone to help here

If you disband a unit while in training you'll get compensation for the workers and how much the unit would cost (metal/oil) without overhead (so can be costly late game when you've got a high overhead).

If you disband a unit after training, you will only receive the workers, no compensation for the metal and oil costs. Infantry will give you one worker, Vech will give you 2 workers, Tanks will give you 3

Thanks all.

So maybe useful to save some workers if you expect to have your army exterminated?

yes it is a good idea if you do not think it is worth the damage it is going to cause the opponents army