This election the house will have 55 voluntary departures + 2 people resigned so far. Assuming ~90% get relegated which may be high that's easily ~100 new members. It varies quite a bit but 2010 for example was down to 85% that won their races.
Few things in life are more predictable than the chances of an incumbent member of the U.S. House of Representatives winning reelection.
They don't provide a number but eyeballing the chart, I think that number starts with a "9" over several decades, and is increasing. Here's an article that says it was around 96.6% in 2014;[0] it must be embarrassing to find yourself in the bottom 3.4 percent of any group.
(It also says House members are reelected more often than Senate members.)
