There is also the devaluation of Sterling against the Euro to consider if Britain pulls out of the EU. Parity is likely to be the consequences. So any Sterling investments would have to go before that occurred and UK pensions would have their value considerably reduced.
It would be a disaster for most UK ex-pats in Europe who largely would not have any say in the process. As if they have not been clobbered enough in the last few years this is likely to finish them off.
I have no doubt they will all have to return home.