The Senate as a body is at risk of losing some members over the next several months. Senators have some significant risk factors:
Senators have excellent health care resources available to them at low to no cost as a major protective factor.
Over a fourth of the Senate is over age 70. A seventh are over age 75.
Senators are temporarily replaced by appointments made by their home state governor. Most states will allow unconstrained choices to be made by the governor. I would assume that a Democratic governor will appoint a replacement level Democrat and a Republican governor will appoint a replacement level Republican. When the governor and the senator are from the same party, that will not shift many if any outcomes in the Senate.
However of the Senators over the age of 70, there are nine Senators (2 Republicans, 7 Democrats/aligned with Democrats) whose home state governor is from the opposite party. The Senate could swing wildly depending on the health and mortality of some Senators.