Fury wasn't immune to conventional harm, as evidenced by them fact that Cap. Britain and Co. were able to "kill" it after its fight with Jaspers. Given that, Monarch has more than enough firepower to beat Fury or at the very least, make him exhaust his energy reserves via attrition.
Or, Fury could simply breach Monarch's armor and tank the universe-busting explosion that results.
Fury was addapting to Jasperīs Warp, the Fury was addapting on the fly, it was taking a big toll on him, I donīt know if Monarch could also tank what Jasper was dishing out, but anyways, here the Fury starts fresh and a fresh Fury could one shot both Cap.
he tanked 238īs explosion, he is very durable, but donīt know if he has the fire power to kill Monarch, but given time he could find a weakness