The group could have been over after dude left
I think they would have still be ok with Eddie as lead after Ruffin left. But, they would not have had the same commercial success and Gordy would have, in turn, invested more in the Four Tops in the early 70s or maybe even invested more in the Spinners or not let the Isley Brothers leave the label.
It's amazing when you consider the talent Motown had during those years. So much talent that they had to literally let some of it just walk out the door.
Could have had a roster with the Temptations, Stevie Wonder, Jackson 5, Supremes, Marvin Gaye, Four Tops, Smokey Robinson, Isley Brothers, Spinners, etc. in the 70s!