IBM would have still made the PC, only using another CP/M clone as OS, and would have owned that market because the other vendor wouldn't have written as clever a deal as Gates did. Two possible outcomes of that: either IBM would have replaced microsoft as center stone of the PC market and been no better and probably worse than microsoft (they were considered pretty evil in their day), or more likely IBM would have failed to create the PC platform (because that was really Microsoft's doing), and the personal computing market would have remained deeply fragmented on both hardware and software levels, tools for gamers and tinkerers but not business computing. In either case, OS/2 wouldn't have happened in the way that it did (especially since microsoft was a key developer behind that). Linux would have had a significantly tougher time happening, either because of IBM's control of the PC market (including the hardware), or in the fragmentation scenario because the lack of a hardware standard would have made it more difficult to build a community of OS enthusiasts. Apple would have probably gone bankrupt during Jobs' wilderness years. Without ms office propping it up as the only desktop alternative to DOS/windows it wouldn't have stood a chance given how incompetent apple's management was at the time.
So, maybe microsoft slowed down the personal computing market, or maybe they sped it up, or maybe they didn't change the timeline at all. I reckon there's no way to tell unless you have a time machine.
I wonder if Gates feels guilty though. His current efforts are laudable, but it always seems like he's compensating for something.