Hi Mika,
In Standard, when you do the TECO work order, notification will be completed. There will be a Completion tick, which will complete the notification.
Is there any specific why you want to keep the notification open after TECO of Order ?
Refer below thread, your abaper can do it.
The SAP Fan Club Forums • View topic - Complete notification during order TECO
Also check whether you can do via User Status.
Regards
Terence