TUI have a strategic decision to make now ( if not been done already) that the MAX will be written out of the S19 schedules and to source replacement a/c, and/or try to utilise their own fleet as optimal as possible to cover the shortfall of up to 9 x 189 seat a/c just in the UK
6 MAX are parked and 3 more were due soon to join TUI UK
That loss of uplift is around 150 flights (departures) a week (based on a conservative 2.5 rotations per day)
They simply cannot attempt to re-jig the schedules in mid season, even if (and very unlikely) we see the MAX certificated again sometime this year.
The press reports that 2 or 3 EU airlines have taken their MAX out of the summer schedules and UFN and AA in the USA have canx 7100 flights (24 a/c)
Ryanair MAX200 were due for this summer - not happening now.