I suspect that between new Congresses, given the turnover in people, that there is a lower likelihood for prior bills to pass. However is there a rule on this - are bills that have not passed in a particular Congress automatically ended (/required to be resubmitted) if not enacted within that particular Congress?
Yes, a bill exists only during the Congress in which it was introduced. I'm not actually aware of a provision in the rules saying this, so you'll have to settle for the Clerk of the House of Representatives.
When does a bill become "dead" or no longer open to consideration?
A bill may be introduced at any point during a two-year Congress. It will remain eligible for consideration throughout the duration of that Congress until the Congress ends or adjourns sine die.