The chance is low (since you haven't done anything like load an XCI, install an NSP, or run homebrew), and I assume you haven't encountered an error/crash screen while running SX OS. These 4 things are the HIGHEST RISK actions.
- If you have any wifi connections set up, turn off your router, and then delete all wifi connections on the Switch. Do this ASAP. As it seems "continuity" is also important to Nintendo, as someone has been banned before for clearing their logs
- (i.e. if your Switch sends any new logs, and these logs "go missing" i.e. they're not present in your NAND backup, then it could be dangerous... so the top priority is to go offline ASAP before any new logs are made and/or sent to Nintendo)
- After that, make ANOTHER NAND backup using Hekate 4.2. This is for SAFETY, as Hekate is the only one that verifies that the NAND backup, to make sure it is not corrupted. People have had BRICKED Switches from restoring NAND backups made with tools other than Hekate. This is a SAFETY nand backup, but it is NOT a CLEAN nand backup.
So what you want to do when you're gonna resell it is restore the first backup you made with SX OS (this is the "hopefully clean backup"). If it bricks, restore your "safety backup" made with Hekate.
Also don't forget to backup BOOT0 and BOOT1 as well.
And until you restore that NAND backup, NEVER go online ever again.
This is the safest you can get, but the ideal was to make a Hekate NAND backup BEFORE loading any CFW.
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EDIT: Also, if you plan to upgrade your firmware version in the future (e.g. a new game requires version 7.0.0), read up on how to upgrade without burning fuses (it's just by using ChoiDujourNX). Because you will want to not burn any fuses in the future, if you want to be able to use your original NAND backup in OFW.