I'm sure I remember reading about a fight that had to have a replacement ref due to the first one suffering exhaustion from heat
As mentioned it has happened before. It is very unlikely any world title bill will only have one referee. And even if that happens, it is still quite possible one of the judges would also be a qualified referee. Even if that is not the case, it would still be possible the supervisor maybe a qualified referee. If the worse came to the worse, the fight would be declared a no contest.
Not a high profile fight but a high profile ref. Mario Ramon vs Bobby Williams 1947. Benny Leonard dies in the first round of the 7th bout he is reffing. The fight was ended and declared a no contest.
Strictly speaking, Goldstein's collapse from SRR-Maxim wasn't an injury. One that was though, in a less high profile bout, occurred when Randy Shields accidentally slugged referee Tom Kelly in the ninth round of his match against SRL. Ringside judge Harry Cecchini relieved Kelly to referee the tenth and final round.
Yes in 1952 during the Maxim / Robinson fight referee Ruby Goldstein wilted from the heat collapsed and had to be replaced by another referee, Ray Miller, who as a fighter once kod Jimmy McLarnin...Ray Robinson, not to be outdone collapsed also in the 12th rd...Joey Maxim ?. Fine...
Sugar Ray Robinson punched a ref accidently in one of his fights too. much like in Whitaker-Mayweather, the ref shook it off...