Depends a lot on the species of tree used for the bonsai. If it is a deciduous type, try gently scraping a little bark off on one of the stems. If this is still green then there is every hope it will reshoot if treated carefully. If the shoots are completely brown and brittle, it is likely to be dead, though it might just grow new shoots from the base.
Some bonsais can be decades old, and some are recently planted. Depending on how old and valuable your bonsai is, I would say that if the main stems are dead it's probably not worth conserving it, as you would have to build up a new framework of branches from scratch anyway if it regrows from the base/roots.
By the way, three days is nothing ... you can't expect reactions from a tree in less than several weeks. So perhaps patience and taking care not to overwater now, is the best policy.

I'd have done the opposite - whenever I have a plant that's flopped and completely dry (or dropping its leaves if its not supposed to) I immerse it in water for 30 minutes or an hour, depending on the plant and size of pot, then remove and leave to drain.

I agree with Bamboo ,a good soaking and a good drain,just make shore that it can drain freely,

If it is a deciduous type of tree it may not be dead but will not re-grow leaves until spring. Keep it moist and wait until June before chucking it on the compost heap. Good luck!

Thanks everyone that is a great help! jen

I was given a bonsai last year. It wasn't happy at first but it thrives now. It went through a sulky period where it dropped 90% of its leaves. Now it is happy as it has got used to its position and temperature.

thanks very much. I'll just let it acclimatise and hope for the best.