Work life is like ladders. Every good step of yours will take it higher on the ladder. This means you will be away from the lower steps as you go up and will eventually have more number of steps below you. If you fall in love with one step, you won't be able to go up and might be someone stepping upward may have to step over you. This may hurt you or throw you out of the ladder.
The art of growing is to create something for the followers/team-members to take over (Effectively). This also need your effort to help grow your subordinates to be able to effectively take up your role, so that you can rise up and take a higher role. Do not have hard feeling about letting go a project. If you are a true leader, it will not go away, but you will be at an abstract level on top of this.
OOAD fits here too, it becomes abstract or generalization as you go up.
What you should focus is how effectively you can mentor the team that will take care of the project and ensuring that any future queries from them be resolved and also ensure that they need to bother you the least for specific things, but may take your advise on broader things.
This should make you feel stronger, in-control and efficient. This will also reflect your competence to the management in the most positive way.
Do not keep hard feeling or obsessions for the work you do and pass on. Lefe is all about achieving milestones. Sitting on a milestone does not take you further.