Allah aza wa jal is both Most Merciful and Severe in Punishment. Allah is most merciful because all the good in the world including mercy comes from him, including any mercy you have on others, that is also from Allah. It is said that Allah created mercy and split it into 100 parts, giving mankind 1 and keeping 99 for himself. So the mercy of all mankind, given by Allah out of his mercy, is 99 times less than Allah's.
At the same time he is Severe in punishment, only punishing those who deserve it. Criminals will complain about the punishment although Allah, out of his mercy, gave them a chance in this life to mend and repent. Had he willed he could have thrown all disbelievers into hell upon creation, but he doesn't punish without warning.
In any case, we Muslims benefit from those who reject Islam as well in the hereafter. Every human has a predestined place in hell and heaven, and their actions drive them to one of them. If people, such as yourself, die rejecting Islam, then your predestined place in heaven will be inherited by the believers, that means, we Muslims will be taking your property in the hereafter.
Likewise if you become Muslim then we also benefit, especially if you are guided by another Muslim, that other M uslim will earn all the good deeds and reward you earn without it detracting from your record.
The Muslim wins in every situation.