Your friend should dump the 2010, and use that money to get a CPO 15 with the EA288 if he wants to stay in a diesel.
No sense in fixing a Gen 1. And no, they wont fix it with a delete. You err, your friend, needs to sell it back to VW and move on to a 15 or something else.
There's a big difference in the EA288. Much better engine. Do yourself a favor and get the upgrade at VW's expense. Plenty of CPO 15's are coming on the market now with low miles. I'm picking up a 15 golf this weekend, most likely.
Much better engine? And you know this how? That super long track record?
Not saying it does or doesn't run better or it is or is not full of improvements on paper. But I think it will take a little more than that to warrant a claim of it being a "much better engine". I mean, the BEW is by most standards not better than the ALH it replaced, yet we certainly did not know this when the 2004s were only a year old and had 25k miles on them, did we?
And in the case of Jetta sedans, one could also make the argument that a 2010, which is still a Golf with a trunk, is a better
car than the NCS Jetta. And what possible problems could the 2015's SCR system present in the future? The few that had it prior didn't exactly have a stellar track record (nor have some other makes, for that matter).
Not trying to make a decision for the OP, just trying to present him... or, ahem, his "friend" with all the facts to make an informed level headed decision that five years from now he may not regret.
To answer the original question, though, the car will need to be stock and in working order with no MIL (so all of its equipment in place and working) before the fix will be instituted. Then you can of course install your delete again, and motor on. That part, of course, will once again void any emissions compliance warranty, but if you delete it all, you won't need it anyway.