I don't mean to belittle your great achievement with license annoyances so forgive me if this sounds harsh, but I won't look twice at any software with an online requirement, if internet connectivity is not an integral part of the software itself. I do realise open source can be a dark, unthankful place that will not pay bills for most developers so this is not about the cost itself.

Unfortunately, pirates almost always have it easier than paying customers, since license checks will probably be removed. Though this is hearsay (anyone?), there was "legal piracy" (no, there's no such thing :P) in the license-via-printer-port-dongle-era, since the dongles sometimes failed at the worst of times (e.g. live recording at a studio). So some users/studios bought a license to be legally covered on paper, but used a pirated version.

I live in a "well-connected" country, but a traveling a few kilometers in the wrong direction leaves me in complete radio silence, and sometimes work (academia) has required me to stay at such places for a couple of days. Since you know Rust, I can (and have had the need to) add `--offline` when building, with required crates locally cached. I know many researchers with the need to bring high-tech equipment + software to remote locations for work over many weeks, sometimes months. The need to find a city just to do a software license check would be crazy.

Unfortunately, I also don't have a good solution, other than trying to trust your customers. An online check once, at install, I can possibly live with, even if I've had to do reinstalls from local files in the field as well...