Yes, it will complain loudly, you can then delete the files and download the (hopefully) pristine ones from the service.
@p314 I’m not sure if restic is the right tool for this particular job. It’ll cut files into smaller blobs, and recombine them into files again, which are then stored on the local disc in the repo (which you then plan to sync to the clolud service). There may be many files needed in order to restore a particular file. The easiest would be to use a service which restic has support for, either directly or via rclone. Then you could just use restic to downloaded the needed files for recovery.
It sounds like an encrypting file system (encfs, gocryptfs, or something similar) may be better suited for your use case. There you’d have a 1-to-1 correspondence between source files and encrypted files.
In order to find out I’d suggest trying restic (and anything else that may work for you) on a small subset of the data. Then simulate all the scenarios that you’re interested in. Shutdown your machine, and try to restore data on a completely different machine for example. Or delete a file (or move it to a different directory) and try to restore that. It’s the only way to find out if it’s going to work for you 
You could do that with restic, but that’s not the way it was intended to be used. Most of the code assumes that files could be downloaded from the storage location on demand, and will fail if something is missing (that you need to place there by hand, a manual and labor intensive process).
If you can get restic to access the remote location directly, it’ll do that for you. It’ll only download the data needed to restore that single file.
I don’t know what AEScrypt does, but we try to make restic as secure as possible. Here’s a short review of the crypto code and design, in case you’re interested in such things: restic cryptography