When India launched their nukes, Pakistan would probably nuke India, fearing they were being targeted. Article 5 gets triggered and every NATO member is at war with India, which might involve nuking them, might not. Russia would probably launch their nukes in response to NATO countries firing their nukes at India because, again, they'd think they might be being targeted. If NATO didn't launch nukes and just carries out a conventional attack on India, Russia probably doesn't get involved militarily.