Gah...bands....this is what being in a band is like I'm afraid, at least that's my experience during 30 years of being in and out of them. You get a great band, you get a great set, and everything ticks over lovely for a few months, then someone gets the hump and leaves, and the auditions start.
If I had the techno gumption, I'd set myself up at home and record solo stuff, demos etc. I'd much rather that than play live, I love the studio. However I'm far too thick and lazy to sort all that out for myself, so I carry on in the band, waiting for someone to leave.
I'd stick with it and see where it goes. It's a pain I know, but if you like the band and the set, then I'd hang in there and see if a drummer comes along. Generally drummers are [i]fairly[/i] straight forward to find, singers are the worst, if you have a good singer, hang on to them with a vice like grip. Finding a great singer is a nightmare.
Life on the road eh?