After a total hyd failure in a Canberra B15 and ejection was not considered necessary (by the crew - but it
was suggested by the rapidly assembling team of experts in the Tower) both navigators and the pilot made the seats safe prior to the wheels up landing (without foam). As the seats had very limited low level, low speed capability (age robs me of the details) the pins went in on long finals. This meant that the escape would not be marred by an inadvertant seat firing.
As Jig Peter said...
if I'd been faced with putting an aircraft down wheels up, and especially if away from an airfield, I think I'd have preferred the seat(s) to be safe