Yoshimo's Heart ?? what to do with it?
is there a way to revive yoshimo after he dies when meeting irenicus?

You have to give it to the temple of I-don't-remember-which-God, the one in the town near the Asylum : Yoshimo has told you to do so.
As I forgot to do that myself, I don't know what happens next.

SPOILER
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I gave it to the temple of Illmater above the Copper Coronet and got HEAPS AND HEAPS of experience.

(SPOILER)
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Copper Coronet ? Thanks ! I have been cursing myself for ages for having moved to the Underdark without taking care of this cursed heart ...

No worries dahlin' (said in thick Ozzie)

can you still get the heart if you dont have yoshimo when you meet irenicus? is it worth bothering about?

No you can't get the heart if he's not in your party when you meet Irenicus. The quest ends with the temple so all you're missing out on is a bucketload of experience (not items etc) so I personally wouldn't worry if you can't do it. If you can, it's sort of like compensation...
Play on mate!