Redis is no longer free software

It is difficult to make specific statements about what might or might not matter. There are at least a good ~200 jurisdictions in the world that may have an opinion on the matter, but I'm not aware of any relevant litigation, statutes, or case law (which does not mean they don't exist!), so the best I can do is make educated guesses.

My gut says that you can probably get some kind of damages out of a permissive license if you're the copyright holder, even if you're not the person attributed. It's hard to say how those damages should be calculated, and different jurisdictions will have different formulas. Here are some formulas that I could imagine being used:

* Determine the market cost of producing the software from scratch (i.e. "hire [n] software engineers for [k] [weeks/months], and pay them market salaries"). Possibly apply some multiplier or discount to it (which is probably going to be a highly arbitrary number in either case).
* Determine the market cost of advertising equivalent to the attribution. (No, I don't know how they would figure out what kind of advertising is equivalent; probably they would ask both sides to submit proposals and the judge would choose between them or come up with a middle ground.)
* Attribution (to someone other than you) is worthless, so you are only entitled to nominal damages (i.e. not very much).
* Attribution is priceless and/or easy, so you are entitled to specific performance (or some reasonable approximation) even though the license doesn't call for it explicitly.
* In some jurisdictions, authors benefit from a separate legal regime called "moral rights," which specifically protects attribution, and that would have its own system of remedies. However, this theory would make the previous version infringing (since you are not attributed there either), and I'm not sure you want to open that can of worms. Note that in most jurisdictions, moral rights are either difficult or impossible to waive, and it is almost never possible to waive them implicitly (i.e. without the license having very specific legal language explicitly referring to moral rights). On the other hand, some jurisdictions have no (or very limited) moral rights.