You cannot indefinitely ask employees to do more for less money. According to law and job contracts you can only do so much unpaid overtime. Usually 10h instead of 8h, and only when justifiable. Everything else is illegal. Paying 60% and working less is hoping for the environment or situation at the market to change, whether or not that is realistic.
However you look at it, sitting at home doing nothing is not the right approach for engineers to get their company back on track.
If there is no money to pay them, they should get shares in the company. So if their R&D is successful, they participate in the outcome.