However, I'm really scared that with the new sets that the Pokémon company will make expanded XY on.
Why are you scared? No one is putting a gun to your head to make you play an older deck, right?
I didn't think VirGen was a top pick for Expanded right now, so unless you think recent results will lead to a resurgence, you can always just
not pursue the deck.
If your income is such that you cannot afford to invest in VirGen as a "fun deck", that isn't too bad; again it was just for fun. If you need it for competitive Expanded play, then it all comes down to how well you expect to perform at events; if you think you're a good player and that it will be make a big showing soon, then the deck may be able to pay for itself, even if Expanded rotates.
Which brings us to paranoia over rotation. This is the last day of March. Unless you only play sporadically or we get a bizarrely early rotation, you've got
four or five months as of today to enjoy any cards that will rotate from Expanded play. If I counted correctly (and I may have messed up XP), there are 21 weeks before September 1st. So even the person who plays two hours per week has about 42 hours worth of game time coming with anything they purchase in the next few days. Not a huge amount of time, but if you're okay buying your typical video game, that you'll play for about as much time over the next five months before beating (maybe utterly completing) it, probably shouldn't sweat a deck. Well, assuming you are spending about the same on both.
(Yes you can resell video games, but most aren't worth that much, used, 5 months later).
Expanded has
never rotated any sets so far. It is possible (but not guaranteed), that TPCi will maintain it for as long as they think they can.
Unlike Standard play, where they have only failed to rotate sets
once over the last 16 years.
If you are playing for fun with your friends,
you can use older formats. You could even see if they were interested in the Legacy Format; just because it was created for the PTCGO does
not mean people cannot use it in real life.