No, there isn`t always a way to avoid death. If you fail your Save against a suprising Save or Die Effect, you`re dead.
If a rouge fails to disable a trap, and it goes off, there was no real way to avoid it ...
Anyway, I decided, for my campaign:
The first time your character is lost "beyond repair" or you decide to retire him (because he doesn`t fit in the campaign, you are bored by the concept and want to try something new...), you can roll up a new character of that level. (But be aware that the character has only the minimum Experience Points for the designated level, so he might still be behind the others).
For further deads, the general rule is average party level -1.
There are some problems if you let replacement characters start at severely lower levels:
a) The player feels that his character is to weak, and can`t contribute much to the game. This lessens his fun.
b) When I design adventures, I am assuming a certain party level - it sometimes screws my plans if the characters are to weak to face the challenges - it is especially difficult if only one character is a few levels behind the others, because the others might have little problems with a certain attack, while this poor character has little chance...
c) If a replacement character dies, and you still follow the same rule, you will end up with a character that is only there to die again or stay at home.
I experienced these problems as a player once - I was still a bit unfamiliar with D&D, and this might have been the reason why my first characters died, but when I was approximately 4 levels below the average party level (without me), I felt useless. Luckily, my DM allowed me to bring up a higher level character...
Oh, besides:
It is a game - no real reason to punish someone if you only want to have fun
Mustrum Ridcully