planeswalker- Kiora on the battlefield and played Hydra and creature gained 7, does the counters fall away when planeswalker die
No. Bioessence Hydra Has 2 abilities that grant counters. The first is a replacement effect that gives it counters as it enters the battlefield. It doesn’t do anything else after that. The second is a triggered ability that gives it counters when planeswalkers gain loyalty. It never causes you to lose counters though. 

Counters always stay on a permanent unless a specific rule or ability says to remove them. Even though the number of counters here is initially based on the planeswalker’s loyalty; there is no rules connection between the planeswalker and the Hydra.