The dividend is easily covered based on past cash flows. Future sales when coupled with interest and debt rollovers could be an issue - as you note primarily because of the low spot price of coal.
It is also worth noting that any increase in coal spot is likely to be eaten up by the railroads. When you have several willing sellers but only one monopoly transporter the transporter is going to bleed you dry. For coal to get a fare share of gross revenue the railroads have to bid on coal ==> less coal must be available than demand.
A dividend cut would be a smart move. The current yield is 3.7%. If ACI moves up to 20 that is a 100% return. If it goes to zero that is a 100% loss. The dividend is just not worth it in a tight cash situation. Perhaps the board can leave a 1c/q token dividend.