Hi cyrus_costa,
Since you can run multiple simulations and mesh computations at the same time, manually cancelling a run or mesh computation should always be the last option regardless of how long it takes. Going forward, please report the ongoing simulation run, if you think it would not cancel on its own, although that is usually very unlikely.
These usually do finish at some point though. Take a look at this forum topic, for example: Unreasonable results
The project has similar warnings as yours, but it does finish. It only means however, that residuals need to be checked for individual levels of acceptance and mesh needs to be improved for the next run, if required.
Cheers!