What happens if you are fit enough to reach Rinjani’s crater rim but cannot finish the summit?

Nothing dramatic happens, provided the arrangements were made before the trek: you stay at the rim camp with agreed supervision while the summit group climbs, and you rejoin them when they return. Plawangan Sembalun, the usual staging camp at about 2,639 meters, is itself a campsite, so declining the push is different from abandoning the trek. Many people make exactly this call, for knees, cold, altitude or plain fatigue, and it is a normal part of mountain life.

The fine print has to be settled at booking, not at 2 in the morning. Ask your operator to specify, in writing, where a non-summiter waits, whether a guide or porter stays at camp with that person, whether the group continues to the lake afterward or returns the same way, and who escorts someone who needs to descend immediately. These are staffing and safety questions, and every operator answers them differently depending on guide-to-guest allocation and the day’s conditions. No park rule establishes an entitlement to be left alone at camp, so never assume it.

Money follows the booking, not the mountain. No verified park rule or standard operator practice gives a price reduction for voluntarily skipping the summit, and your booked permit days stay purchased, so ask for the operator’s on-mountain change and cancellation terms in advance rather than expecting a refund at camp. A medically necessary evacuation is a completely different matter from choosing to sleep through the summit attempt, and insurance conversations should distinguish the two as well.

Altitude honesty belongs in this answer, because the summit should never outrank symptoms. The standing guidance is to tell your guide and turn around if a headache persists, or if symptoms progress to vomiting, poor balance or confusion; the summit is optional and the mountain is the point. It is also worth knowing that authority can change summit plans for everyone: a park notice has previously closed the rim-to-summit segment during an evacuation even while other sections stayed open, so even fit trekkers can wake to an altered plan. Treat the summit as a bonus layered on a trip that is already complete, and the decision loses its weight.