I've been testing this for the past week, and I can pretty confidently say RCS messages are not [always] saved to your phone's database.
I know RCS messages are supposedly saved as MMS into your phone's SMS/MMS database, mmssms.db. And that has been true for years.
Sometime recently, Google changed this to no longer be the case.
If I receive an RCS message, it'll show up in Google Messages. If I then clear the app data for Google Messages, the received message will be gone. It will not come back, even after 48 hours (the most I have waited is 96 hours/4 days).
After receiving the RCS message, I have waited varying time periods, sometimes over a day, before clearing the app data. It will usually disappear but sometimes will stay. I can't tell what the difference is between the persistent and non-persistent messages.
I have even received RCS messages, did a backup using Android's built-in backup to a Google account, and then I cleared the app data. The RCS messages do not come back.
Interestingly, if I send an RCS message, then it will be restored after clearing the app data. Almost instantly. It will, of course, be displayed as an MMS message.
I tested this on a Samsung S24 with previous versions of the app as well as the current beta version.
I have also used a couple of third-party apps to check, and the messages are just gone. I used SMS Backup & Restore, Super Backup & Restore, as well as SMS Import / Export. All of them show the same thing, that my sent RCS messages are saved but not my incoming ones.