Once you are on Universal Credit you will stay on Universal Credit.
Even if you start work, as long as earnings are low enough, the Universal Credit award will simply be adjusted as your income changes.
If any change means your income is too high to qualify, the Universal Credit claim will remain open for 6 months, so any changes in circumstances can be taken into account in these 6 months. If you re-qualify you would not need to make a new claim.
When your circumstances change, you they must report this to the Universal Credit Services Centre telephone line on 0345 6000 723.
If you receive Council Tax Support you should also notify the Council of the change.