No, it’s not correct. Close, though. The second clause needs to be “would have,” rather than “would,” to match the tense, which sounds like past subjunctive to me but could also be present perfect subjunctive.
If you use the conditional in the first clause, the second clause is contingent on the same condition, and should also be in the conditional to match:
If he would meet some scary fish, he would return to the surface.
This makes sense if you’re describing his standard operating procedure or something like that. So, one context where this sounds natural and idiomatic to me is:
Every day, he used to dive into the lake. If he’d see some scary fish, he’d come right back up to the surface.
This describes an event that actually happened, on occasion, over a period of time in the past.
Another way to express a similar concept is with the subjunctive mood, indicating that this is a hypothetical or counterfactual situation.
In the previous example, if whoever we’re talking about had never met a scary fish, it would be a counterfactual clause in the past subjunctive, and the dependent clause would be a past conditional. (Observe that if [he] had never met is a present perfect subjunctive and would be is a present conditional. This is very similar to your example, but works for me while the other doesn’t, possibly because the other example sounds counterfactual, and this is not.)
If he had met any scary fish, he would have returned to the surface.
An example of a hypothetical situation with the future subjunctive (which is actually sarcastic):
I’ll be going diving soon. I promise, Mom: if I meet any scary fish, I will return to the surface immediately.
Note that the first example says “some scary fish” because it’s implied that there were some, and the second and third examples say “any scary fish,” because there either definitely were none or none are expected.