They've said that you will be able to retrain talents, though it won't be as easy as it is now. Currently, they've made it pretty easy to respec talents because they want people testing different combinations-- all you have to do is pay a fee to a trainer and off you go. When the game releases, you'll still be able to retrain talents, but there will be some kind of difficulty involved. That's as specific as they've been.
With regards to specific talents, they're not all spell-specific. In fact, quite a few of them aren't. As an example, I did a quick analysis of the warlock talents. Out of the available talent choices, 22 are specific to one or two spells, 19 are more general (affecting multiple spells are the warlock as a whole), and 9 were just new abilities. However, this analysis is a bit misleading. The spell-specific definition of "one-or-two spells" may not affect your concern. Talents that afffect two spells may still be safe, since the odds are slim that both spells will be nerfed significantly at a single time. More importantly, only about half of the spell-specific talents can be buffed with a full 5 talent points; most of the general talents can.
The upshot: don't worry about it. Even 'losing' talent points as you describe won't hurt your character overmuch. Remember, a lot of these talents are relatively miniscule bonuses-- 5% here, 10% here, and so on. They're meant mostly to promote individuality and certain playstyles, not define whether a character is broken or not.
Finally, I doubt that Blizzard will be making enormous nerfs once the game is released. Tweaks, most probably; Blizzard tweaks relentlessly. But most of the classes that have talents are going into more of a stable period now. (Exception would be the warlock. Hello, Infernal and Felhunter, see you next patch!)