re: They'll keep 'em going as long as they're alive
Yeah - there's at LEAST six months of funding in place now - and to be honest - theres every chance that they'll keep going beyond that time.
If they do - they'll further funding again.
At the point they become non-mobile, I imagine a low-level operation will be put in place - to monitor seasonal change and run it almost exclusively via UHF instead of using the DSN to monitor beeps etc.
Doug