No, he won't regret that for the rest of his life. He will regret it temporarily but he won't bring that forever, he might bring that for a long time but I doubt that he's going to regret that forever.
He's going to remember how reckless he was and that's for sure.
That's just money, you can earn money but if you lose your health because you can't live a normal life anymore, that's bigger than the money you lose. Losing big money is not good, but we can always move on and live our life, try to improve our life financially by working hard, and be positive going forward.
There are gamblers who lose a lot of money due to addiction, but eventually, they beat the addiction and live a normal life, some people even still able to return in gambling but more responsible.
I won't say "that's just money". We don't know how he worked hard for that but it's also his fault for gambling that amount within a quick time frame.
The impact mentally that it has given will be there but if he wants to recover, he shouldn't let that disappoint put him into that situation forever since there's still a way to recover it through working and other legitimate means.