If you own a copy of Trainz then your username StefanWeiser is tied to your ability to use the software so deleting that account will mean your software will be unusable. However, if you are OK with losing access to MyTrainz services then the MyTrainz Agreement says under section 2 MyTrainz Account,
(d) You may close your account by submitting a request to https://support.trainzportal.com
There are hundreds if not thousands of diesel locomotives to choose from representing nearly every corner of the world.
There's no reason to delete your account. N3V doesn't do anything with your account if you have it active and when you have time you can always start up Trainz again and either keep the current version or upgrade to the next version if you wish, and there is no cost for keeping your account.
Many of us here have been here 20-years or more with many people taking time off and away then coming back again when they have time. There are many forum posts about coming back after many years with questions on how to do things because the program has changed.
WOW! Thank you, I just have concerns about what happens to my account when I don't use it, maybe I'm exaggerating. I will look in from time to time. Regards!
