TDD,
Generals (and below) who found themselves 'sacked' were usually given something else to do. Some, by dint of being rather elderly, were retired (or allowed to return to retirement if they'd been 'dug out' for war service).
For instance, from World War 1:
Sir John French was, to all intents and purposes, sacked as GOC of the BEF in 1915, but this was presented as his being given a new job as C-in-C home forces.
Sir Edmund Allenby was sacked as GOC Third Army because Haig didn't like him; after a short period, he was sent to Palestine (where he did rather well for himself). In similar vein Horace Smith Dorien was sacked as GOC of Second Army because Sir John French (qv) disliked him. Again, after a short period, he ended up in another job, although not on the Western Front.
In contrast: Sir Hubert Gough was removed from command of Fifth Army after the German Spring Offensives in 1918. He then spent a year kicking his heels before being given command of the British military mission to the Baltic.
Lt Col John Ford Elkington was sacked as CO of his battalion after arranging their surrender (I can't recall how he avoided capture) in 1914. He was court-martialled, sacked from his command and cashiered, although there was some sympathy for his position, since it was more complicated than the prosecution suggested. He then enlisted in the Foreign Legion as a legionnaire, did some rather heroic things and was awarded several gongs. His record was so distinguished that he was restored to his original rank by the Army and awarded a DSO...
In World War 2, commanders might find themselves with nothing to do, but something else was usually found for them, even if they did go from commanding brigades to being GOC Paperclip Purchasing (South West) [hypothetical example].
Which is a long-winded way of saying 'it depends...'