What happens if sciatica is left untreated?

Depends on the cause: Pressure on the nerves can occur for a variety of reasons. If it is herniated discs pressing on nerves going down your leg, you can develop pain, tingling and even weakness. It is best to relieve that pressure, as soon as possible. This will decrease your pain and allow the nerves to return to normal and weakness to improve.

typically resolves: Sciatica pain is often self-limited and resolves over time with conservative care, including physical therapy and anti-inflammatories.

Usually Improves: Typically it improves within 3-6 weeks on its own as your body heals. If it continues then many different things can happen, chronic pain/numbness, muscle wasting from disuse or atrophy from significant nerve compression. In more severe cases, things like bowel/bladder incontinence or even paralysis can ensue. Would suggest seeing your doctor if you are not improving after 3-4 weeks.