In short: yes, this would suffice under common circumstances. Of course you cannot get your data back, but it would prevent the program from launching again.
Reimaging usually replaces all programs on the C: drive and resets Windows and its settings completely. The list of programs to be executed upon startup is in system files, so reimaging will prevent the malware from launching unless you click it again.
If user data is kept, if there is another drive, or if the malware came from something like an email attachment, reimaging will not replace those files. If you accidentally click it again, or if the malware has embedded itself into other files that are not replaced by reimaging, then you will be reinfected.
In a very obscure case, it might also have embedded itself into places like the BIOS or other firmware, but I have not heard of mainstream malware doing that so that would be very unlikely. (If this were the case, you would probably have to throw the hardware away; but again, I have not heard of this happening yet.)
If your disk image is simply a backup, then be careful that your disk image does not contain the ransomware. Backup your backup before you operate on it!