Can an employer terminate my employment while on w.c.

There are several laws that might impact your situation.  There is nothing unlawful under PA workers comp law about terminating an employee who is out on workers comp.  Workers comp does not require your employer to hold your position for you.  There are some exceptions but that's generally the rule.  If you were given FMLA leave and you followed applicable rules notifing your employer that you are ready to return to work and can return to your former position without restrictions or modifications, then maybe your employer violated FMLA.  Maybe a law protecting workers with disabilities would offer some protection to you.  I'd encourage you to contact an attorney who can go over the facts of your specific situation and who can give advice that fits.