I replaced my rear bearings at about 160K miles. It was not urgently required and gear oil was staying where it should, but the option of having one grenade on a long trip was unappealing, so I chose to do it on my timeline. Seals too of course. The tech section has all your answers.

When I removed the bearings, they did have some barely noticeable play compared to new, but were not close to failure from what I could determine. But my confidence level is that much higher now.

-Bill
'87 4Runner w/ '96 5VZ-FE, 'Red Chili II'
'97 Taco XtraCab 3RZ-FE, 'BlackBean'
TLCA # 13257, Rising Sun 4x4 Club Land Use Coordinator
"He who stops being better stops being good." -Oliver Cromwell