If a mage is moving through earth and not getting anywhere quick enough he will die, cause he didn't return to his body...

And he even has no possibility to return to his body in a quick way...

But if he ever critically glitches he is instantly returned to his body without any greater harm (besides a heavy headache...)
This seems somewhat strange to me...

It's ridiculous for all kinds of reasons. The first spell any serious astral explorer will learn will be a Stun Self spell. Drop your counterspelling and let yourself have it. You'll be unconscious, but at least you'll be instantly back in your body, instantly escaping from that mob of bound force 6 elementals that were waiting in ambush behind that ward for you... And with no way to track you back!

I may be mistaken but I believe that all spells in astral do physical damage.

I have not found that rule in SR4, I think that's old SR3- thinking seeping through into SR4. This happens to me a lot...

What he said wasn't true even in SR3. It used to be that drain for spells cast in astral space did physical damage. If that's the case in SR4, they forgot to put it in the books.