Re: "what do Rockstar really loose? [sic]"
Perhaps you haven't had a great deal to do with employment tribunals, but the compensation that is awarded to those who are judged to have been unfairly dismissed can amount to some weeks or months salary, which if there are a significant number of individuals involved will certainly add up to a "hefty chunk of money".
I would also question your assertion that workers wouldn't want a tribunal case showing up for fear of jeopardising future employment - perhaps they would rather just leave the (now published in public) record of them having been dismissed for 'Gross Misconduct' to follow them around. Failure to contest it would surely imply acceptance of guilt.
We appear to only have the point of view from the Union/workers side though, and there is no specific information as to what the nature of the Gross Misconduct was, but discussing ways to improve the workplace on Telegram certainly won't be considered sufficient for summary dismissal by a tribunal, even if they had been bad-mouthing the company or its management in their posts. The UK has some fairly strong regulations governing both the reasons why and the procedures for, dismissing staff. The scope of things that allow summary dismissal is relatively small, and even then it has to be done by the correct procedures. Without a clearly justifiable (and serious enough) reason for immediate sacking, there are a sequence of witnessed verbal and written warnings that have to be gone through for repeat offences before you can hand a troublesome employee their cards.
I suspect that this may be (once again) a US based employer who either doesn't understand that other countries do things in a more civilised fashion than the USA, or they think because they are based in the US, they can do as they like. If that is the case, I think they are going to get a rather sharp and costly awakening to the reality of UK/European employment laws.