Hi @Syed Zaffar the 7.3 LTS EOS is until Sep 24, 2022.
For EOL we cant give you the exact date as Databricks reserves the right to completely remove a release version from the API at any time after support ends, without prior notice.
However the version should be available atleast for a couple of months after EOS. It would be better if you try to migrate to latest LTS to avoid last min huddles. I would say sooner the better.
https://docs.databricks.com/release-notes/runtime/10.x-migration.html