Henry Huggins, from Luton, had been in a coma for 19 months
A man who stamped on the head of his unconscious victim after a row about a dog could face further prosecution.
Henry Huggins, 48, from Luton died earlier this month after being in a coma since the attack on 8 August 2013.
Stuart Docherty, 40, was jailed for 12 years in November after admitting causing grievous bodily harm with intent.
Police said the case may be referred back to the Crown Prosecution Service after a post-mortem examination.
Mr Huggins was attacked outside his Luton flat by Docherty and his friend, James Early.
James Early (left) and Stuart Docherty were jailed for their attack on Henry Huggins
Early had confronted Mr Huggins, his neighbour, about his dog - which they had previously argued over. A row followed and Mr Huggins was punched to the ground.
Docherty, of Townsley, Luton, then arrived and stamped on Mr Huggins' head.
The victim suffered serious brain damage and remained in a "persistent vegetative state" for more than 19 months.
Docherty was jailed at Luton Crown Court where Judge David Farrell QC described his involvement as "an appalling act of cowardice and violence. It was a heinous and grossly wicked act".
Early, 40, of Whipperley Ring, Luton, was convicted of assault causing actual bodily harm and jailed for two-and-a-half years.
Det Insp Fraser Wylie of Bedfordshire Police said: "We are aware that Mr Huggins has sadly died.
"We are awaiting the results of the post mortem and the matter will be referred to the Crown Prosecution Service should any further action be required.
"We are keeping the family updated and our thoughts are with them at this difficult time."
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