You cannot be compelled to remain a director and if you wish to resign, you are quite at liberty to do so.
If you have shares in the business, then you can sell your shares or keep them as you wish.
You say that you loaned the business 16,000 pounds.
The business is indebted to you for that 16,000 pounds assuming that it was not the purchase price for the shares in which case you have shares and you are not entitled to the money back unless they want to buy the shares from you.
In respect of your personal guarantee for the leased items, you obviously remain liable for that if the limited company doesn’t pay.
You cannot get blood out of a stone in the worst scenario is that if you press for the 16,000 pounds, the remaining directors liquidate the company, you get nothing, and the landlord and the lease companies foreclose and you are all personally liable.