Poor form. Regardless of the decision itself, you don't do it by text, it is a shameful way to treat someone who has been around the Wasps experience for so long. There may be another side to the story, you don't treat people that way full stop.
If he's a contractor, then he should have known before because he'd not have signed a contract.
If an employee then that's a lawsuit.
He is a contractor. I recall him talking about it all when Covid lockdown began. Wasps cancelled the contract at that point. I guess they choose not to offer him a contract for this year. He would have known he did not have a contract long before now, but maybe nothing in writing. In fairness, how many contractors who submit bids to do work get contacted to say they didn't get the contract? Welcome to the modern world. Brutal.
I know that I'd have been in touch quite a while ago asking for a contract. And certainly not expect one the day before the season starts, without even being aware if his schedule was free.
If Wasps never confirmed they'd not be hiring him back, that's not amazing, but it's a long way from the suggestion that he's been dumped the day before the season starts. He was dumped over a year ago if for covid.
I can't say I understand the people who say that they'll not go to games without him though. Did they offer to do the same with players and coaches? Medical staff? His is a voice that I'll associate with Wasps always, but that doesn't mean he's the only man they're allowed to hire to do the job.