Even if he cheats, he won't find anything here.

You know, each of you is partially right. Situations like the one described are certainly annoying and need to be addressed somehow. What if you wrote directly to such a player: "Either you think you can beat me – then come and beat me NOW, or you see that you're losing – then surrender, but don't drag it out! Because while I'm wasting my time with you, I could be playing a more interesting game for me with an opponent of my level." (The last part is optional – only if the young man doesn't understand what you're unhappy about.) In general, such behavior by weaker players shows either their young age and, as a result, their inability to admit defeat, or complexes ("pride prevents them from admitting it").
But simply abandoning the game without explanation (even to a schoolboy) is not right. Only if you're playing without rules outside the community – but then your opponent could suddenly "disappear in an English manner" as well.

Regarding cheaters, I wanted to suggest something earlier: we need to fight this somehow! More than 1700 "smart alecks" is a lot! :(
In an ideal world, you could make manual registration only after passing a qualification (here's a save, win in 1-2 minutes with a screen demonstration). This would weed out obvious degenerates like the one with 50,000 angels (and CheatEngine?), and those who only started playing yesterday and don't even know the game. Or make login through social networks. Or link the account to a phone number. In a more extreme, fantastical scenario – login through a government services portal! :) Then a banned player wouldn't be able to simply create a new account, and then – the 10th, ... 20th, ... 100th...
And also, maybe it's worth adding a button somewhere in the menu on heroes3.tv in a prominent place: "List of cheaters / Wall of shame"?