I have been solo mining for a couple of months now.

A few weeks ago the machine that was hosting bitcoin running in -server mode on my network had a hardware failure, so I just started up bitcoin on a different machine and redirected all of the clients to that one.

It just occurred to me that the original machine had been crunching on a block for a couple of days and should have been quite near completion!  I've resolved the hardware issue and have it back online, if I redirect my clients back to the older server will it continue where things left off, or has that block expired or timed out in some manner at this point?

Thanks,
-X

Nope. Think of each hash as playing a lottery ticket with a (difficulty * 2^48 / 0xffff) chance of winning.