O.k. Let's get some things straight. Both Dembele & Holtby are class players. Dembele went off the boil through various injuries, and from losing his most effective midfield partner - Sandro. Holtby is young, and has come from a completely different league. However, you do not get to play for the German national side if you are an average player. I think we'll more of him next season. Dempsey, I would agree about. Although I'm not sure he was ever on the boil. Useful squad player - no more.
Where would the money be spent? Well, I would hope on two top class strikers to start with. Had we had at least one last season we would have finished comfortably in the top 4. Also, not so much would have been on Bale's shoulders. We could also use a top notch attacking/creative midfield play - who can score a few goals as well.
Of course it would be impossible to replace the threat that Bale poses to any side with one single player. You can, however, buy 2-3 top quality players who all pose a threat. That gives the opposition more than one player to worry about.