The Colombian-born Vargas, a former North American champion, had already been put down himself when he stunned Khan and the capacity crowd.
In Birmingham, Khan took lead by dropping his opponent Samuel Vargas with his blurring speed of hand in the second round, the former light-welterweight world champion was then floored himself, but recovered to win by a unanimous points decision.
The pace finally settled down as the fight entered the championship rounds with Khan continuing to be in control for the most part but still looking vulnerable to the overhand right which gave a bloodied Vargas some hope.
Both Khan and his English rival have insisted they still want the fight, but Brook's last appearance was at super-welterweight. The rounds in the bank will do no harm but the defensive issues remain and that ensures any fight involving Khan remains must watch.
Khan returned to the ring following a two-year hiatus in April, when he demolished Phil Lo Greco in 39 seconds.
But Filipino veteran Pacquiao is demanding more than £10m to travel to the United Kingdom to face the former world light-welterweight champion.
Hearn believes the Pacquiao and Brook fights will generate similar figures but revealed Khan will earn more for facing his fellow Brit because the Sheffield star will accept less than a 50/50 split.
"The rumours were that he pulled out of that because he couldn't even make 154lbs, so him making 147lbs is just a line he is using to get the fans back again, or win the fans over". It was his first fight in almost two years since an injury.
"The fight against Vargas will be tough but I've prayers and support from everyone". Khan staggered backward but was saved by the bell once again.
He added: "It could be one year, two, five or six".
"There is only so much we can do; we will listen to the public, we know Amir wants Pacquiao and he will fight Brook".
A clash with his old adversary Brook has also been touted, however, Khan has suggested that a clash with the Filipino superstar would be preferable.