Did the acquirer know about the status of your patent. We assume so. All that has been evaluated by the buyer and accepted as some future value. If you now want to rewrite the deal so you get "upside" which means retaining some present value in a future asset then you'll have to determine whether the acquirer also ascribed the same value you do to that asset.
If not (they don't care about your patent's ability to demand royalties from an infringer and don't think that's anything they'd do) then you may have some ability. The problem is that if I had acquired your company then I wouldn't want you to control whether one of my larger competitors got a demand for royalties. I need to control that process and not let prior shareholders be able to create business uncertainty. Who knows... maybe they'll counter sue for something. (I have been through this btw and it costs about $100K per month to litigate... for at least a year... without a trial!)
I would take the money... be happy... and move onto a more productive next project.