If you mean "what drain current will not damage the device?", that
will not be found in the model except as crude imax, imelt warning flags.
Externalities matter to a lot of "reliability stuff". Like, a common thing will
be to break up a wide device into fingers such that electromigration
will not be the failure mode. But that will have very different end-optima
depending on whether you will market the part as commercial (70C,
plastic pkg), industrial (85C, low cost ceramic / high temp mold compound)
or mil / space (hermetic ceramic). Jmax will be way lower as you go hotter.
But the process physical data, the as-processed worst case of all that, the
reliability studies that give Jmax @ temp for X years service life, all reside
elsewhere and the designer's job requires pulling it all together from the
wherever they may sit.
But somebody probably has put sandbagged rules in the layout design
manual which should be part of the PDK bundle.