the right thing to do is to actually ping the original reporter if possible, or a developer that you might assign the bug to and try to drive it to a conclusion.

if the answer is 'everything in that part of the code has been rewritten' or 'yeah, that was a dup, we fixed that' or 'there isn't enough information here to try to reproduce it even if we wanted to' or 'this a feature request that we would never even consider' or some other similar thing, then sure delete it.

otherwise you're just throwing away useful information.

edit: I think this difference of option is due to a cultural difference between (a) the software should be as correct as reasonably possible and (b) if no one is complaining then there isn't a problem

Closing bugs because of a rewrite is probably the most harmful practice in the whole industry. The accumulated unresolved issues of your existing code base are a rich resource of test cases. Writing the new code base without checking to see if it fixes the old bugs is a mistake.