Assalamu Alaikum
We do not know who goes to jannah or hellfire, EVEN IF they are Muslim. Muslims get a taste of jahannum too, don't they? Or is the mention of jahannum only for play? We're all sinners here.
Secondly as a Muslim one HAS TO have the belief that Allah is the MOST JUST, MOST WISE.
YOU and anyone else will NEVER come close to His attributions. Understand that, internalize it, and never forget it. So whatever empathy or sadness you feel for someone else, it means nothing compared with Allah's attributions and His closeness with His slaves. With that being said, a person's deeds and faith is between them and their Lord. Therefore, it's NONE of your business what happens after they die. They are with their Lord, you cannot and will never be involved in Allah's judgement of another soul.
If you worry about nonbelievers going to jahannum, then do what you can while they are alive. That's incumbent on all of us: to give dawah. But you can't spread the message if you're in this little cloud of yours where your worries are the afterlife of someone else and not your own. You will not even think of anyone else comes judgement day. You'd be blessed if you're still sane.