Jungle would become essentially irrelevant in that case unless given compensation buffs
As a jungler its still relatively safe to pull a gank with 1/2 HP. So for it not to be safe you would need to be under 1/2 HP. Think of the implications of being under 1/2 hp after Red, blue, and wolves.
Jungle becomes nigh impossible to clear. Riot it forced to give compensation buffs to the jungle XP and gold gains. So now they can start to hard farm and come out of the jungle level 18 when everyone else is 14. Shyvana and Yi become meta again. Hard farm till 18. 1v5.
Right now jungle is in one of its healthiest spots. The jungle diversity is fucking insane. You can play pretty much anything right now and make it work.
Also lets think about what jungle actually does. Its a stupidity punisher. If you play like a moron that jungler is gonna get ya. Most junglers gold and below dont feel comfortable forcing ganks. They just take the ones that are free. (and trust me. there are plenty) Now you do see the occasional forced gank (which almost always ends in a tower dive) But those arent as common unless they are specific diving junglers (elise, Level 6 Kayn, Level 6 Skarner, etc)
Also heres the thing. Laners decide the game. not the jungler. If the laners play smart, ward, and keep track of the jungler it can be infuriating to play against. The jungler just cant make anything work and he is forced to sit in his jungle while the enemy jungler gets to gank. Jungle is entirely dependent on stupid plays from enemy laners to get ahead.