> Your license defines exactly what software it's a license for, I guarantee you "pirated copy" is not part of that.
That's where DMCA anti-circumvention exemptions come into play. If I own an IP license for software X; but there are technological barriers in place preventing me from using the software for the purpose I paid for the license to enable; then computer programs that "fix the problem" to allow me to use the license I paid for, are explicitly a protected class of software under the law.
And the license, or Terms of Service, or anything else, can't say anything to the contrary (or, well, it can, but such terms would be legally unenforceable for reasons of public policy — similar to e.g. contracts stipulating that workers will work without legally-mandated protections, or a contract from a public educational institution granting access to a resource but not to legally-mandated accessibility aides for that resource.)
And that is enshrined explicitly in multiple existing exemptions related to abandonware, which would pertain in exactly the case where a service like Steam goes defunct and all the licensing schemes of its distributed games stop working. The various cracks to get those games working again? Legally exempt!
> multiplayer still requires their servers
Given that two existing DMCA anti-circumvention exemptions are:
> Computer programs that enable wireless devices to connect to a wireless telecommunications network when circumvention is undertaken solely in order to connect to a wireless telecommunications network and such connection is authorized by the operator of such network;
and:
> Video games in the form of computer programs embodied in physical or downloaded formats that have been lawfully acquired as complete games, when the copyright owner or its authorized representative has ceased to provide access to an external computer server necessary to facilitate an authentication process to enable local gameplay;
These clauses, read carefully by a competent lawyer, could be argued to in combination have a spirit that would extend to include a new exemption: of alterations to online games required to allow them to connect to the "telecommunications network" embodied by a white-room reimplemented private server for the game.