should be safe if you printout the sourcecode (some html and vanilla javascript) of the revery tool, too. thats all you need for a recovery.

there is a good chance, that the 2017 apk will not run on phones in 10 years.

in your scenario you use coinomi just to create private and public key pairs without using all the other fancy functions. so it would be better if you use the recovery tool right now to show the private keys of your coins and print out the keypairs for your safe.