Actually, I would go so far as to say that it 
doesn't look like that tape is attached to the 
background AT ALL anymore. Look at how you can no 
longer clearly see the background color behind 
it. (Even if it is a bit tough to tell from the 
shine of whatever took the picture.) There's no 
way to be sure (short of asking the seller), but 
if it were still stuck, I suspect the background 
color would be more easily visible through it.

Startyde, I think that tape has probably degraded.
If you like the cel, I would say go for it! ^_^

I always discard the tape when I can, but if you 
want me to find some of my cels that had been 
taped to their backgrounds, I can make you some 
up-close scans of what the background looks like 
when degraded tape has been removed. I'm pretty 
picky, and even I don't think it looks terrible. 
It definitely doesn't detract from a cel with an 
image I love. ^_^ It might help you decide if you 
want to bid on it. Let me know. ^_^

Many Sharp Smiles,
--Drac