It's pretty hardy and goes dormant. You only need a few alive to grow a healthy starter back when you need it again, so every now and then I make an extra amount, mix in a little more flour than normal, spread it in blobs on an aluminium foil-covered baking tray and stick the whole thing in the freezer. After a few hours I come back, pop them off the foil and into a freezer bag.
When reviving, I try to use two blobs from two separate bags just in case one has died. I put them in tepid water for a bit, then add flour and mix and I'm back in business.
My starter was given to me by Dan Lepard[1] (the end-boss of breadmaking) during a sourdough masterclass that I was given as a present. I thoroughly recommend this as a present if you have a friend or loved one who is interested in making bread btw. It's fantastic and you get payback in tasty loaves for many years.
If it's just a few weeks, I've found the fridge to be fine. It will take a couple of feeds over 48h to re-activate completely, but it's otherwise ok.
If you start from scratch, you can get going in 3/4 days if you're willing to throw in a bit of honey or maple syrup at first (1tsp). Without it, it does seem to take a week.
Freezing doesn't kill bacteria, it's actually how biologists preserve their samples. Most yeast you buy in a store (e.g. Fleischmann's) are better if you freeze it after opening for best quality.
To be fair, when freezing bacteria in a lab, you usually add glycerol to help avoid ice crystals (which is the thing that would kill the bacteria in the first place). That's not something you'd necessarily do here. However, so long as the dough mixture isn't too wet, I wouldn't see why it couldn't be frozen as-is
At one point in the past, I dried mine out and put it in an envelope in a drawer. I was able to reconstitute it from this at a later point. The starter I have came from here: http://carlsfriends.net, for anyone interested in sourcing their own.
I tried it based on stories I'd heard about old timers using it as the mortar in log cabins between the logs, and later reconstituted. Don't know if anything really survives or not, but I was able to get it to rise and make bread so...
