You may not have to replace the actual wiring and the panel case and power/ground bars because they’re usually aluminum or coated or plated....however, you’ll likely have to replace all the breakers and the main breaker....
I’d strip down the panel and remove the breakers and mains and look at the distribution bars, ground lugs, etc...I’d inspect the power mains cables coming in...are they aluminum, or copper? Were they coated with No-Ox? etc.....
You’re best be is to have an electrician look at it; he’ll likely do what I’ve said, any way....depending on how bad, dirty and how long it was under water, he may recommend changing out the guts of the whole thing....
Agree. A good visual should tell you more. But if you do replace it, damage it beyond any future use by “recycling” scumbags.