Oh, very 
and what a shock to find.
Guinea-pigs do hide things well, you are right. I've had GPs go to bed 100% and come downstairs in the morning to find them dead.
Or (as in the case of my little Abby boar last year) subtle signs.
We had GP1 alone for 6 days , GP2 died on the Sunday, I phoned a Rescue and arranged to see a piglet. They were getting a surrender of (IIRC) 24 males on the Thursday.
GP1 slept in my DD room in his big cage but went out to the Pighouse by day.
Cleaning and steaming the Pighouse to remove every trace of my GP was hard (both symbolically and physically).
We introduced the boys in a brand new paddling pool (they'd had a 'bond' at the Rescue but we put them in two boxes to drive home. GP1 wheeked the whole way, but I couldn't give my DD the responsibilty of a squabble to deal with while I drove)
Your pig will need a few days to re-adjust. Then you can make sure he's fit and well.
If you want a boar, you can either ask a rescue to bond (they might have an amiable adult boy) or get a piglet (we got a 6 week boy, who is now a huuuge ten month boar)
Our GP1 GP1 was always very boary and coped well with a new boy.
If I have to match my young boy up at anytime (close your ears GP1) I'd neuter GP3 rather than give him a piglet (he'd bonk it 
)
Your remaining GP knows his cagemate is dead, which at least is closure for him. Our boys were being cuddled when GP2 died and we put them both in the Pighouse that night, we didn't want GP1 to think he'd find his brother alive in there if he looked hard enough. It didn't seem right to sneak his body away (but we did the next morning, he was a bit niffy)
I did a couple of threads about getting our newbie last year,
(A warm but hushed welcome - about July/Aug if you need any ideas)
Good Luck and another furry To The Bridge