How can I recover this barleywine batch?

You can't (shouldn't) go back to the mash tun after the boil.

My guess is that you would get some tannins instead of more sugar.

As for why you got a lower OG, perhaps it was something on your mash? - Grains crushed too coarsely? - Mash temperature? - Mash style (batch vs fly?)

Since by now you are probably already on the fermentor, there are only 2 things you can do:

1 - Leave it as it is and enjoy a good honest to god beer (probably over 6%)

2 - Add more fermentables to it, either LME, DME or sugars to reach your planned OG, at the risk of the flavor.

I would go with 1 and leave the barley wine for the next batch.

By the way, which book are you following?

1.060 will make a perfectly acceptable beer (albeit not a barley wine), BUT your bitterness to gravity ratio will be way off. The perceived bitterness of a beer is dependent on the starting and finishing gravities. A high gravity beer finishes sweeter than a low gravity beer, and that sweetness reduces the perceived bitterness. If you hopped the beer with the intention of getting a finishing gravity around 1.025 and your beer actually finishes at 1.014, it will be more bitter than you intended.

That's a long winded way of saying that, in order to create a balanced beer, I'd use DME to bring the gravity up closer to your target.