The card Nature's Revolt is out, then a mountain and is declared as an attacker, then the enchantment is destroyed.
What happens to the mountain? Is it still attacking, can it be blocked e.t.c.
The mountain will be removed from combat; which means it stops attacking, blocking, etc.
506.4. A permanent is removed from combat if it leaves the battlefield, if its controller changes, if it phases out, if an effect specifically removes it from combat, if it’s a planeswalker that’s being attacked and stops being a planeswalker, or if it’s an attacking or blocking creature that regenerates (see rule 701.14) or stops being a creature. A creature that’s removed from combat stops being an attacking, blocking, blocked, and/or unblocked creature. A planeswalker that’s removed from combat stops being attacked.
Yes, the card can be blocked. The card would count as a creature, that in this situation, is attacking. Unless you decided to enchant it or use a spell that causes otherwise, the land would be able to be blocked, as well as block.