Someone mentioned how unfair and cruel it would have been if Steve just came back in time to let Peggy know he was alright, have a dance with her, and leave. I've been considering this, and I realized that I don't agree.
In my early 20's, I had an intense relationship with a man. My family moved me to a different continent (it could have been to a different time) and I didn't hear from him for 30 years. He informed my later relationships, I had his picture on my desk at work for years, and I did always wonder what happened to him. When we met again, he was married, a SAHD with 4 children under 6. We talked, he apologized for being distant, less than faithful, and unkind. He had actually followed me to the country I had moved to, and tried to find me. We're not friends - his politics are not mine -- but I'm forever grateful for what he did to complete the past.