I've never actually had a source block just.. disappear on me.
If you want to really overengineer it, use golden waterproof pipes as stated earlier. Put a gate on them to detect liquid traversing. If the accumulators ever stop, send a signal to an autarchic gate on a wooden waterproof pipe hooked to some kind of water reserve (rainwater tank, RC tank, etc). That should give you plenty of time to fix the vanishing water source blocks.
On top of that, use 4+ deployers with a bucket of water such that there is always flowing water touching the accumulators. One deploys and another one sucks its water back up. Less room for error, right?! Kidding.