It's not a good idea to keep progressing until failure. Sometimes it happens, but if you can anticipate it, it's better to stop just before and modify the program. This is where a coach comes in handy; they can look at your sets and assess bar speed in the context of all the prior sessions and make programming adjustments before things get dicey. If you are on your own, you'll need to try and monitor your fatigue and recovery and make the switches yourself. Ultimately it's not a problem to be conservative and switch a bit too early; you'll still keep moving forward to that next new weight, it just might be a bit slower of a march at that point.