If you leave the loco sitting there it will may be jittering between the two blocks which will not do it any good and may well do damage, so fix the problem asap.Operator errors are a given. If a train is crossing blocks and momentarily receives current from 2 power sources, how likely is it of burning out the train motor? Are there "easy to install" fail safes I can install in the circuit - similar to switches in a modern home that trip if a spike is detected?The likelyhood of a motor burning out if it receives power from two different controllers is about zero. It is the controllers that will need to be protected in this case. The wheels and pickups will effectively bridge the two sections, connecting them both together, so the motor is fine but the two controllers must be able to survive having their outputs connected together.
It is for this reason that it is important to use separate power supplies, completely isolated from each other (as per your last diagram), to prevent unexpected current flows when the train crosses between controllers.
If you choose your controllers well (i.e. with comprehensive output protection) then you should be OK.
No doubt you could also add circuit breakers to each section output for extra protection. I haven't researched protectors for DC (I'm planning to use DCC) so I will defer to others for advice in this area.
The controllers should be OK if they have good heat sinking.
Yes, separate supplies but the controllers should be connected at the negative of the rectifiers (the earth symbols on the diagram) this will get those locos with diagonal pick-ups (Lima, Hornby etc) smoothly across the blocks. ALL blocks MUST be double isolated, NO common rail.
The controllers chosen have output diodes so should be fine provided they have good heat sinking.