It would be best and easiest to remove the RW SIM from the phone AND the RW app, inorder to make use of the eSIM for Fi as Fi is its own app and having the RW app installed may cause conflicts with the new version of the Fi app and its Enhanced network features that work on the Pixel 3.
If you are gone less then 20 days, then I would just leave your RW service as it is active, then you can “come back” just by deactivating and removing Fi, and putting your RW sim back in the phone then reinstalling the app and re-activating the phone.
Phone calls to RW number will go to VM. Texts will not be delivered normally. It will be as if you phone is off. Texts however, you can install Republic Anywhere and get your RW texts that way.
If you are not porting or transferring over your number to another carrier, you are not switching out of Republic. You are just using the phone on another carrier per its own unlocked capabilities. U can still have active service with any company and swap other SIM cards into the phone.