Hi Bill, welcome to Tomatoville!
I've never grown BHN 602, but according to the info at Tomato Growers Supply online catalog, it is a large, red, round slicer or canner with VFFF resistence to various diseases. There is nothing wrong with using next generation hybrid seeds or volunteer seedlings, they will produce just fine. However, at the genetic level, they will not be exactly the same as your original hybrid. Without knowing the parents that went into creating BHN 602, it's not possible to predict what you will get, but when dealing with round, red hybrids, it would be surprising if you did not get round red fruit when you grew them out. It might look or taste very similar to your original hybrid, or it might not!
You won't know til you try, so give it a go if you have the curiosity and space.