Depends which part you're looking at:
1. Telnic is using Neustar's infrastructure for the root .tel servers so there's already proven operational reliability and robustness there.
2. For TelHosting you'll have the choice between using Telnic's infrastructure, or another TelHosting provider, i.e. your registrar. This is the authoritative part of the system for adding/removing/modifying records, and for hosting the web proxy. Switching between providers will most likely be pretty straightforward.
3. If some of those nameservers go down then the network ought to adapt, and if all go down then your .tel data should still be available, because it would be distributed throughout the DNS network (so long as caches are primed somewhere along the way).
4. The friending system is the only centralised part of the system from what I understand, but it's certainly the least critical part.. in the worst case scenario an outage shouldn't mean the end of the world.
I'd also add that both Telnic and TelHosting providers have strict service levels to meet; for more information read,
Technical Requirements for TelHosting [PDF]
Couple of wild thoughts:
1. Might somebody put the TelHosting part into Amazon's EC2 cloud?
2. Could you strategically place anchors around the world that periodically walk through every .tel zone, ensuring that caches are always primed everywhere? Pretty crazy

Second thoughts, that would be extremely abusive!
Maybe Justin or Henri can chime in to correct anything I've gotten wrong or missed..