I'm not so sure that it matters much from an international angle - at most they'll be missing out on perhaps preferential roaming rates, but I'm not even sure they will miss out on that - for the most part, the different international networks of t-mobile/orange/voda all seem to operate completely independently so I wouldn't be surprised if each subsidiary has to pay full whack to the other for roaming.

They might lose out if they have to drop the Orange/T-Mobile branding because of the public flotation but I would assume they would continue to license them. They're already split off into a different company from the others in the Orange/T-Mobile groups now that they're a joint venture.

As for whether DT/FT would want to offload it - DT seems to be having a tough time at the moment (they even had to flog T-Mobile USA) so they might be looking for a way out. FT has put a lot of effort into the Orange brand to just drop it, though.