I have seen quite a few threads where people say the electric 4wd actuator has failed on them on both the 4runner and the Tacoma (which does not have multi-mode but some models did have the electric-button 4wd selector.)
If I understand the 99-2000 Multimode T-case was a modified J-shifter with a 4wd button on the shifter. From 2wd with the shifter in the top-left position, pushing the button engages the 4wd with the center differential operating (i.e. unlocked.) This is the AWD mode. Then, pulling the J-shifter down to the Low-Left position locks the center diff and keeps the front axle engaged for "conventional" 4wd. Moving the J-shifter to the right and up then puts it into N and continuing up to the top-right position puts it in 4wd LO.
On this t-case if the electric actuator fails, you lose AWD capability but can always run it in "conventional" 4wd mode by pulling the J-shifter down to the low-left position (I think!)
However, the 01-02 models did away with the J-shifter and have a simpler, 3-position shifter with the 4wd button on the side of the shifter knob and the center-diff lock button on the dashboard (where the rear diff lock button on a 96-2000 would be.) In that one, the button selects 2wd or 4wd and if the electric actuator is inoperative, the only way you can get 4wd is to pull the shifter straight down into low (and I don't even know if that would work or if it would just put the vehicle into 2wd Lo-range - anybody know?)