Would Russian gangsters really let him go for money?

You aren't a criminal, and you're wrong.

This was essentially a tax. You simply can't clip a police officer without an extensive investigation and pressure. Only when it's an absolutely needed example can you sanction that type of extreme.

Further, there isn't a person with the title of "a mafia". Most wiseguys from all walks (from the Yak boy in the parlor to the bratva soldier watching a warehouse) don't have a lot of money. After you factor in payroll, personal expenses (which are typically a lot), bribes, merch expenses, etc, you don't have a lot of money.

Anyway. He killed someone who was probably useless in the organization. That demands a tax.

I doubt professional and ruthless criminals would be that stupid. Their first job would be to take care of the dead guy's family, which would be important for loyalty among the rank and file. Revenge is for dummies, and they couldn't take the money and shoot Alonzo too or nobody else would pay up in future.

you can either have 2 guys and no money or one dead guy and a million dollars.

Maybe they intended to kill him anyways, but it's better "business" to take a tax, then to just simply rub a guy out.

Plus the possibility of a dirty corrupt cop on your payroll or in your pocket is far more valuable to the organization.

That is terrible business model. You would have massive internal problems if that were the case.

Yeah that system is pretty ancient, and basically isolated to one part of the world. It doesn't surprise me however, that the Arab world still uses a similar system to this day :)