They are very susceptable to damp so the cage should not be on the ground .
They can cope with a degree of cold if that's what they are used to but they should always have appropriate company , by that a guinea-pig friend/friends that are a harmonious group , otherwise the bullied one has a shit life and sits away from the herd not able to eat or snuggle . It's illegal in Switzerland to keep one . We only had one when she was the last of our elderly trio (she stayed inside 24/7 ) or if we had a bereaved pig waiting for a new friend
They need to be dry and draught proof .
And checked every day several times a day .
He is very much at risk of being eaten. Foxes and badgers ( badgers are phenomenally strong ) can dig or break in.
The guinea-pig will be bored and very lonely . If its a childs' pet even if they cuddle him a while he's on his own . And I'll bet in winter his care levels will slip.
Domestic guinea pigs are nothing like their rangey wild cousins .
They are the most vinerable creatures and will quickly go down with a respiratory infection. They cannot put up any type of fight . They don't even bite considering they are rodents .
They pee/pooh in their hay beds and are untidy little animals .
DD and I had ours in a wooden playhouse with access from their hutches to the floor . They pootled about , chatted , cuddled up . Inside the haybox was warm as it was insulated but it needed cleaned every day .
In winter they came indoors at night (cool room) so no temperature fluctuations - very dangerous for them to go hot-cold or cold-hot .
If you do pignap him they'll likely get another after they explain he;s run away to a farm .
You could print off some Care Leaflets and hand them over or suggest they might look on some (Guinea-Lynx or one of many Rescue sites give advice )
I had words with my DD school when their pigs were out in November on concrete . Obviously no planning was made for their care and it was Guy Fawkes .
I didn't rant but I did say "I don;t care if you think I am bolshy and interfereing but I'm not going to sleep happily if I know two small vunerable rodents are outside on wet concrete on this weekend of all weekends"
They were moved inside .
Ask your NDN if they'd like to be stuck in the bathroom with a window that lets in the cold . No TV, no phone , no books . Nothing to do . No one to talk to . I bet they'll say "No"