To the first question:
The uboats didn't have a a radar for spotting planes. They had some rudimentary RWRs, but that's it.
The only subs which came with radar were the US one's.
For the Why not diving: They dove allright. Diving takes time and even if the plane('s) arrived after the sub had vanished from the surface, it's wake and the diving position were still visible from above.
to the second question:
The escape-hatches only worked in shallow waters and even there not so well. The exact numbers of survivors... no idea.
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