Actually the salesman is right. I left a huge company once, but left my 401k with them for a year. During that time the employer switched 401k custodians, and the default investment option was a target date fund. Fund collapsed (it was 2008) and I lost 60%. I had originally placed my funds in money market, but the new custodian had the right to change that to target date, its in the laws. DO NOT trust DST with your 401k, Take it and roll it over to a place of your choosing.
This was posted by @RZpojHo-4ywf in another thread, thought more people should see it.