Aside from a random crash, I experienced the following:

The "Ghost Town Gunfight" quest appears to be uncompletable. After speaking to Ringo, he suggests I get "Sunny Smiles" to help.
I head to "Goodsprings Source" to fin Sunny.
When I get there Sunny is not around, however, I do find a red ball...I assume it's a Sunny's dog's toy.
I walk down the path a bit and run into "Barton Thorn." He asks for my help in rescuing his GF further up the path past the broken radio tower.
After I kill all the geckos, I find Sunny's body, her dead dog and the body of "Johnny" at the top of the trail.
"Barton Thorn" walks up, tells me he set me up and I'm forced to kill him.
I head back to town to speak to "Ringo" but the only dialog options are "I haven't talked to her yet." and "goodbye."

My pipboy still lists Talk to Sunny is incomplete but this mission is now grayed out.

Is there anyway to continue this mission?

doesn't sound like it unfortunatley, your most likely going to have to reload a previous save

I had the exact same problem and wondered if it was a bug or just a random unfortunate result of NPCs having more free-will in this iteration. Sonny got killed before I even made it back to the firepit to complete the crafing part of the tutorial. By the time I realized she was crucial for the Gunfight quest I just gave up and restarted from my Doc Mitchell save. A bit of a pain but I was eventually able to complete both quests. Although during the gunfight quest I was unable to find Trudy in order to convince her to join us. She reappeared after the fight though. I don't want to have to race around worrying that quest characters are going to die. That's a bummer.

Overall I'm just really enjoying being back in the Wasteland though.