How about:
You give the disconnected 1/4th of the playtime to get back online.
If he doesn't come back, the other player has a choice, give it a draw or
the computer takes over with a difficulty level based on the disconnected player's points.
If he wins it counts only for half a game, if he looses it still counts for half a game.
I think some people have forgotten that Live Chess isn't a really serious place in which your official rating is going to be affected. Personally, I use it as a practice/experiment field to try new things and further my skill on certain plays and openings as well as handling pressure in time constraints.
A simple 5minute timer would be more than adequate to allow for a reconnect if a disconnect occurs. After 5mins if you don't reconnect you lose. Simple.
Others have stated this timer system in heavy detail trying to please everyone. You really can't for one sole reason, luck. Luck is a factor in disconnections on Live and cannot be justly handled for every player. You get booted from the server, that's unlucky. Your wireless internet router drops it's connection, that's unlucky. Even an outage of internet by your ISP for hours or days is extremely unlucky, but your ISP puts the outage in place for the benefit of everyone, they aren't going to take into consideration your loss of a chess game.
This is how adjournment should be approached, a simple system which is fair to everyone on a general basis. 5minutes to reconnect or you lose. Applies for everyone (maybe extra time for premium members for an added perk for becoming one) no matter their situation.
We have all been at both ends of disconnections and although we are frustrated we get over it quickly because there's nothing that can be done about it. Now we can have a 5minute buffer which is of great benefit to everyone, otherwise accept the disconnection as you would accept a disconnection that happened in the past.
Apply the KISS rule and everything will be sweet. The more we try to put in fail-safe's for every scenario we can think of, the more problems that will occur with it. The simplest answer is usually the best one.
Just my 2 cents.