Does the ubuntu partition automatically get deleted and that disk space allocation is automatically restored to the computer main SSD drive?

Here is an Apple article with instructions for Erasing All Content & Settings which should be the easiest way forward since I believe it will also get rid of any other partitions as well:

Erase your Mac and reset it to factory settings - Apple Support

FYI, it should be possible to delete the Linux partitions without needing to touch the macOS boot volume/container, but I'm not sure Disk Utility will merge the resulting space into your main macOS container/partition.....it may require the use of the command line.

Also, whenever making any custom modifications, it is generally a good idea to first figure out how to undo those changes before you implement them especially when the modification is not easily accessible or provided within the OS GUI interface.

No, it won’t be automatically cleared. You must remove it yourself, following instructions hopefully provided by the same people who told you how to get it onto your Mac.