Your QuickBooks Online (QBO) will only end once you stop or cancel your subscription. This is different from the desktop version, which will only last for 3 years from its released date (i.e QuickBooks Desktop (QBDT) 2017 products will be discontinued this year).
For more information, please refer to these articles:
Imho, there is no end of life for QB Desktop version with a one time license. Company only provides the End of Support policy after 3 years as mentioned by FritzF. You may keep using your QB Desktop for good. Most of the time, our QBD version will reach its EOL once we experienced an unresolved issue for working normally.
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