if my wallet is sufficiently secure, can I ever lose my coins? I've made an offline address and only have the key stored on 2 encrypted flash drives stored in different locations with the private key written physically on paper and stored in 2 locations. Do I ever have to worry about my coins? That is, could theyever be lost in software changes or is that as big of a never-going-to-happen as the 21 million limit being lifted? I'm pretty sure I'm not touching that wallet for a long time. Is there any benefit to repeating this process for a more "fresh" address ever or does that not make sense?
I'll go through your question clause by clause:


  I've made an offline address


You're doing good.


  and only have the key stored on 2 encrypted flash drives stored in different locations 


As long as only you know the password and the password is sufficiently strong, this is probably secure.


  with the private key written physically on paper and stored in 2 locations. 


If either of these two locations are accessible by anyone other than you, then they are vulnerable. If someone else found either paper, and your keys are in plain text, then you could consider them compromised.


  Do I ever have to worry about my coins? 


Yes.


  That is, could they ever be lost in software changes 


Extremely unlikely, as the whole of Bitcoin depends on the safety of balances through upgrades. There are people who have very vested in ensuring that this never happens. Even a bug in the protocol could not erase history in an unrecoverable way, as a single offline client copied online or bootstrap.dat would refresh anyone affected.


  or is that as big of a never-going-to-happen as the 21 million limit being lifted? 


Pretty much.


  I'm pretty sure I'm not touching that wallet for a long time. Is there any benefit to repeating this process for a more "fresh" address ever or does that not make sense?


Theoretically, you would never need to regenerate keys unless some kind of vulnerability was found in the software that generated your key, ala the Android random number generator flaw.

An unlikely occurrence would be some kind of change to the way private keys are imported, and your private key generated in 2013 cannot be securely converted to whatever format is expected in 2063, or whenever. I wouldn't get too paranoid about this.