for what it’s worth, since a couple of years ago, iNat photos that have been licensed (not all rights reserved) are stored over in the AWS Open Data repository. i don’t know for sure, but i suspect that even if the iNaturalist organization completely collapsed tomorrow, Amazon would still keep the AWS Open Dataset up and available for everyone for at least some period of time, if not indefinitely.
so i would guess that all the iNat observations that made it to GBIF (since they are licensed) would still have the underlying image files available. if GBIF were to go down, too, then you still have the AWS Open Dataset’s monthly metadata files. so you could still get basic data associated with the photos – observer, date, location, taxon.
if Amazon / AWS were to disappear… well, then half internet would be non-functional. so there would be bigger problems than missing iNat observations / photos in that case.
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if you want to download your photos, that’s probably fine, but i think realistically, the main scenario that this kind of backup would save you from is if you (or someone who got access to your account) deleted all your observations (or deleted your iNat account altogether) and iNat staff could not undo this for some reason. or if you wanted to put your data into a time capsule to be opened many decades from now, then i guess this would be another scenario where it might make sense to download everything.