You shouldn't lose your virtual unless
1) Your virtual is a boot camp hybrid in which case it probably will work, but I haven't tested it.
2) Your version of Parallels is incompatible with the beta of OS X. Yosemite hasn't caused me any problems with this, but it always seems like the final release version will somehow break Parallels, requiring a paid upgrade of Parallels.
Parallels 7 still works fine for me in Mavericks, although if I was going to do any serious gaming I would have upgraded to 8 for that alone.