It has been mentioned in the extension for 'If you already have leave in the UK and planned to extend your leave when it expires, you do not need to complete this form. Please continue to apply using the appropriate online application form.'
So, I think I have to extend my visa if I am going to leave the country!
Well you can't do that if you don't have a Tier 2 sponsor. You cannot apply for a Tier 2 General extension OR for ILR if you don't have a sponsor or are unemployed.
Please see below as well:
If you’re applying to stay in the UK long-term
You can apply from the UK to switch to a long-term UK visa until 31 July 2020 if your leave expires between 24 January 2020 and 31 July 2020. This includes applications where you would usually need to apply for a visa from your home country.
You’ll need to meet the requirements of the route you are applying for and pay the UK application fee.
This includes those whose leave has already been extended to 31 July 2020.
You can apply online. The terms of your leave will remain the same until your application is decided.
This refers to those who cannot normally apply within the UK to change visas, i.e Tier 2 Dependent applying for Tier 2 General, and would normally have to apply from home country. It doesn't apply to your circumstances.