This means no sales, no themed merchandise, no decorations. December 25 and most other day are treated just like any other day for all stores malls, restaurants, ect.
You’d still get non religious holiday events like mothers days, or independence days.
What whould change?
Now what happens to a religion that is, for the most part, now separated from capitalism?
Really depends on the religion. There are some religions that aren’t organized at all, and are fully self practiced. They don’t require things to be sold.
The religion of capitalism is a different beast though. I would say that people need things to celebrate in life though, or they tend to get very hostile. It seems to me that the more communal an event is the better the effect is on society, as people can set aside a lot of grievances for the festivities.