Hi bazzard,
Altough it was different circumstances I do know how you feel because in October my mum and I went out to get some shopping and coffee and came home to find my dad had died. I beat myself up so much, especially because it had been my idea to take mum out, and asked myself all these questions a thousand times over - was it quick, if we'd been there would it have made any difference, was he scared?
The doctor assured us it was a very quick and painless death and nothing could have prevented it and I do believe him but at the same time I do still feel the guilt every day, just less intensely as time passes. To be perfectly honest, if somebody granted me the wish of being able to say one more thing to my dad, i would tell him I'm sorry we weren't there for him.
God, this post has probably just made you feel worse. i just wanted you to know you're not alone in these feelings.I think in these kind of circumstances, guilt is a big part of the grieving process - it sucks, doesn't it? All we can do is wait for emotions to catch up with the rational part that believes there was nothing that could be done.
Take care of yourself, I'll be thinking of you.