V70 D5 tensioner defective at 104′

Hello all, yesterday at my V70 D5 (AWD Bj 2006 km 104′ the tensioning roller broke, almost paced, the engine went out immediately. The car is now in the workshop, a first compression measurement was ok except for a cylinder (#4) with 20% less. Tomorrow a new timing belt is put on and tested again. Who has experience with this? Can I trust the engine, should it run again? What about the water pump, should I change it precautionly? Thank you for feedback!