I've experienced this too, whether it's a VPN connection that goes bad or a loss in internet connectivity.
I personally haven't found a way to reconnect, no.
Also, I find sometimes the system ends my job, other times it doesn't (but I will end it manually once logged back on).
I have seen this before working.
Basically if I login with the same workstation/session name, it prompts this screen asking "Do you want to connect to the job that is active already?" and then I can say connect to it or start a new job.
I want to be able to consistently connect to that job. How do I do that?
Have you tried contacting IBM and/or the developer of your 5250 software to ask this?
I am curious as to a solution to if there is one. I always assumed I just was dead in the water when this happened. :)
If you find a solution, please post!