Re: Oh well
Same way as it does now?
Battery-backed units in the cabinets/exchanges which provide service for a limited time? We tend to call them UPS in the IT trade. If only someone had come up with a way to UPS IP-based technology, eh?
To be honest, though, I manage a school's IT and our procedures just say "call 999". But in all the meetings we have, we are quite aware that we're much more likely to be able to do that safely from out on the playing field with a mobile phone than trying to call from a landline.
Despite the fact that we have leased lines, SIP trunks, analog and ISDN backups (for emergency calls only), we recognise that we're actually much more likely to want to be OUT of the building before we worry about that. And then if O2, EE, Vodafone and whoever else are ALL down, and we can't pick up the Wifi to SIP-dial, that that's a scenario that may call for extreme action like - going to the nearest house and borrowing their phone and hoping that's not affected.
999 call handling won't change, because the other end is almost certainly IP-based by now, at some point anyway. The call handling centre MUST be IP in this day and age, surely? With analog backups, sure, but it must be IP for the first-hop and local devices?
But to be honest, 999 calls must be literally THOUSANDS OF TIMES more likely to come from a mobile handset nowadays. Because you can flee AND call, rather than have to stay in the emergency area. Sure, for an injury, you could call on a landline but then you're tied between the landline and your patient unless he happened to collapse in a very convenient location.
I think we're being spoiled nowadays, given that only a generation ago, it could have to be a run to the local phonebox (Remember those? Remember the years of being taught how to use them to dial 999?).
I'm not saying they shouldn't provide 999 services and backups and everything else, but surely nowadays calling 999 can be done by one of DOZENS of methods. Hell, Skype even lets you dial 999. I don't see that IP conversion would inherently degrade or change the system for doing so.