I’m no expert here but agree with Andrew that you need to document everything and put your situation and proposal in writing to your landlord.
If you are still in dialogue with them I would express to them that you are sending a letter and that you need them to consider how this will play out.
They can either help you trade through this situation (est. ~3 months from lock-down to possible return to offices) and on the other side they still have a tenant who will always appreciate the compassion shown and assistance provided in this tough time OR they can contribute to an avoidable early termination and have a space that it may take them a lot longer to fill.
Assuming they in turn have financial commitments on the premises then at the very least they should be prepared to have a chat with their financiers about providing them with some relief so all parties can achieve a longer term win-win outcome.
Hope that helps…all the best!