3 ditching O2 as partner?

I have a friend who is on Three, but uses O2 as the roaming partner.

The only mobile coverage is Voda or O2, when they're at home.

Now we've found out Three have ditched O2 as their roaming partner, I think changed to Orange.

Although at present the phone does still work using O2 - will this for ever be the case, or will we one day find the phone doesn't work?

Orange have a mast, but they never finished building it - for nearly 2 years it's been only partly built! (although Orange swear blind it's operational - I'd like to see how when the portacabin housing the transmitter is still empty, there's no aerials and no cables from the mains supply to it, still I digress!)

Thanks.