My
son did the same thing. Then I found a pearl of wisdom, a nugget of hope, just for folks that have found themselves in this situation. Read on at your own peril, as spoilers abound, but be forewarned, it may well be the savior of all those ignorantly blissful souls that missed the big huge honkin' pop up dialog warning:
Spoiler Use the mantis foreleg glitch to rebuild your character. If you don't know how to do this you must
Spoiler take a mantis foreleg from the school house in goodsprings, right out of the doc's house and head up to the cemetary. Lure a radscorpion up to the cemetary and kill it. Put the foreleg in the radscorpion's inventory and remove it. Each time you remove the foreleg, you will get the XP for killing the radscorp.
Do this until you are the level your previous character was (presumably 30), reassign your skill points as they were and select the perks you had. The only thing missing is your old gear, but now you know where to get it so it won't be so bad getting the old kit back together. And if you're just rebuilding your old lost character to play the DLCs, you get your gear stripped from you anyways.
So my son was able to rebuild his old character from scratch, in no time at all (20 min, max), and go play the DLC he wanted to. Everyone was happy. World peace ensued and children all over the world had plenty to eat. So go forth, intrepid forumers, and spread the word: You can rebuild it. Cue old rerun of
The Million Dollar Man.................
-Gunny out.