Tensioner not tensioning. Repair or replace?

Check what derailleur that is and how much a new one costs.

Then, enter the model number on si.shimano.com, refer to the exploded drawing and check how much a new spring costs.

If a new derailleur isn’t that expensive and if you don’t want to take it apart, replace. Otherwise repair.

I was out doing a little trail ride today. Shifted to an easier gear to go uphill, and my chain hopped off the casette into the spokes halfway up. Hopped off, walked up the hill, and noticed my chain was a bit floppy. Not sure if it was like that before it hopped off the cassette, but it would make sense, since it was shifting fine up until this point and had never jumped off before. I was able to ride back to the parking lot, it seemed to have just enough tension if I kept pressure on it.

Got it home and washed it off a bit. Noticed that the guide pulley sprocket wasn’t spinning hardly at all. Noticed there was a little metal nub pressing up against the side of the sprocket (Photo in the imgur link below). Took off the guide sprocket and that nub doesn’t seem to move or have any way of adjusting it, so maybe that’s normal and has nothing to do with this? Just an observation.

Checked out the derailer hanger, and it seems straight.

Anyway, is there anything I can do to repair this? Or is this a “Just replace it” scenario? And if so, can anyone help me identify the derailer I need? I found one on Amazon, but the “SGSL” at the end of the model number is throwing me off (Reddit won’t let me link it, but it’s the first result when searching “Shimano Deore RDT6000SGSL Schaltwerk (10-Fach) “). Took a photo of the model number on mine, also in the imgur link below.

https://imgur.com/a/GnSDrtm