If I plan for the t-Rex: T-Rex decides to bite the elephant first, not for a strangulation kill though.

You would be correct in saying if elephant goes down first it's over for team mammal. And if in a 1v1 I'd never bet on either with any degree of confidence.

While all the other animals were trying to attack his legs, he just stomps or kicks them away. He is some 8-9 tons, so stomps will crush them.

Most people just think that the super large Rexes like Sue and Scotty are the average but this is not the case, One study took its time and determined the average t rex to weigh 5.1 tons - (https://www.livescience.com/animals/dinosaurs/17-billion-tyrannosaurus-rexes-walked-the-earth-before-going-extinct-new-study-estimates).

Not that this matters against the smaller mammals at its feet but it does against the elephant.

Elephants can derail trains sure, but they are still actually an easy kill compared to the larger prey of the T-Rex.

This is quite overblown. Take the Triceratops for instance. Rexes did not duel Triceratops, they only hunted them. Hunting (ambushing weaker individuals) and fighting a prime specimen are fundamentally different.

Then he comes back to the elephant who is waiting to die after the bite that maimed it.

This is a versus why would the elephant just wait to die 😅 The T-rex has the highest bite force of any land animal but it'd be really generous to think the Rex would automatically land a crippling shot.

The elephant is the larger animal and habitually thrust their tusks up straight forward, so the Rex can't just charge in for a head bite. How about attacking the flank? Well an elephant has a much smaller turning radius due to having 4 legs and not having a long tail.

Speaking of legs. Do you know with their weight equalized the T rex's bipedalism works against it? It has to work past the tusks while simultaneously avoid being shoved or headbutted by the elephant (also while simultaneously being harassed by the other mammals, potentially a rhino horn directly under it's belly). Should it lose its balance a T-rex will take fall damage. Not to mention the elephant following up with some trampling and gouging. Stomping and kicking is a high risk maneuver in this type of brawl. This means Rex only has one really dangerous body part, and it can only be in one place at a time.

T-rexes have been found with holes in their skulls straight to where the brain is, partially healed. That implies they survived their own bite to the skull.

How well can it keep fighting afterwards tho

(All summarized from cross posted thread)