That's not a problem if the people in the old team understand that their security is tied up with the success of the organisation. I.e. if the new team does well, the organisation does well, and all employees are cared for.
If somehow the people in the old team get into their heads the idea that organisation-wide success stands in conflict with their security, then you have a problem.
But the problem is with management, not the people on the teams.
Edit: in general, it's a common disease in companies to associate people with teams rather than the organisation. People don't become useless because their previous roles are obsoleted. Those are still valuable people and sure, there's a cost to retraining them, but the cost to letting them go (in terms of what it teaches the rest of your employees) is so much greater. (Though unfortunately harder to measure.)
We can thank Jack Welch of GE for that attitude. I thought the same thing in the 80’s when GE was shedding thousands of employees. That those employees should be useable for new endeavors. Turns out retraining is a cost the company can externalize with firings
If somehow the people in the old team get into their heads the idea that organisation-wide success stands in conflict with their security, then you have a problem.
But the problem is with management, not the people on the teams.
Edit: in general, it's a common disease in companies to associate people with teams rather than the organisation. People don't become useless because their previous roles are obsoleted. Those are still valuable people and sure, there's a cost to retraining them, but the cost to letting them go (in terms of what it teaches the rest of your employees) is so much greater. (Though unfortunately harder to measure.)