If bitcoin mining still works after the latest halving
It works, otherwise no blocks will be generated and Bitcoin will die.
how much can someone invest in the mining of the bitcoin
As much as they're willing to spend.
and how much bitcoin is it likely to generate before the mining plan expires?
There's no thing such as "mining plain", unless you refer to cloud mining which usually scam or not profit. As for amount of Bitcoin you could mine (not generate), it depends on various aspect such as your mining hashrate and Bitcoin mining difficulty. You could use mining calculator to get rough estimation.