Russia does not want to give Belarus and Su-30K, which returned from India after ten years of operation. Instead of providing their allies Belarus, the leadership of "Rosoboronexport" has decided to sell them to Vietnam. But in return for them, experts say, Russia could be able to use the Belarusian military airfields.
I remember an article quoting an Indian official that it still has about half of it's operating life. And no one with common sense will buy a something that will fly only for a "one-time use" no matter how cheap it is given. Heck, even donated defense materials will not be accepted if it's one-time use only. Belarus will also be upgrading it to SU-30KN standards for an additional $5M each.