Re: Did not de-register for L-Permit, still possible to return to Switzerland?
I doubt it, though I guess you ought to inform your previous gemeinde. L permits expire automatically if you're out of the country for more than 3 months usually. Main things I can think of is did you manage to cancel your health insurance and other contracts before you left, you might still owe Swiss taxes, etc.
I assume you're an EU national and not non-EU. Otherwise the rules are different as far as hiring procedures go.