1) Yes, do whatever you need to do to make sure Rip never falls off in BitW, even if it's a crappy one. If you have no choice but to do a 1 CP bite just after SR fell off, then you should do it.
2) If you'll energy cap before you can refresh SR or Rip you should just FB anyway in most cases. Thrashing is a probably a good choice if they're both going to fall off but I don't know 100% what's the optimal way to handle it.