Unless an activity is logistically totally impossible, I would definitely start off with the intention of continuing out of school activities that your DC like doing. Would you be considering giving things up if they were going to your catchment comp / upper school, or does the question only arise because they are going to a more distant / more academically demanding school? If they have any ambivalence about the choice of school, don't give them an automatic reason to resent it
It may be that something 'dies a death' naturally after a while, but as you can see. I am also an advocate the 'suck it and see' approach.
Our year 8 and year 12 DC currently each do swim squad, Scouts and drama groups and DD (yr8) also does Nature Club, Hockey, Harry Potter club and Latin during lunchtime and cricket one evening a week.
And they nearly always manage to get all their homework done on time