I tried for a good while to find a way to get back there. No matter what I tried, though, I couldn't find a way to get back over the rubble. So, unless there's a really well-hidden trick, I'm inclined to say that it's not possible.
As consolation, however:
if you keep pressing onward along the outside path, there's another bonfire not very far away at all.
Human Effigies can be found from Starting Gift, Static Locations (corpses), Merchants (All merchants have limited supply), and NPC's (both given and dropped when killed).
The term 'farm' usually implies an unlimited resource, as you pointed out. As of the latest patch, the Company of Champions covenant allows infinite respawn.
These are enemies that drop Effigies:
- Attack Dogs.
- Skeletons [not in Undead Purgatory]
- Turtle Knights.
- Sentinel (Sword/Shield) and Sentinel (Great Sword)
Always remember you can farm 6 effigies off of the Old Firekeepers and 3 alone off Housekeeper Milibeth in Things Betwixt.
After unlocking the Shrine of Winter, it is possible to farm Smooth and Silky Stones. While not directly farming Effigies, these have a high conversion rate to Effigies at Dyna & Tillo (Drop trade crow), although this is random.
There is however a way to restore humanity consistently.
In the Shrine of Amana, above the last bonfire, there is a Shrine with a praying Milfinito. After you have 'rescued' the two stray maidens (one outside the Demon of Song room, another behind the Embedded Door in Drangleic Castle) you can pray at this Shrine at any time to regain humanity. This is free of cost and can be done a limitless amount of times.
There is an easier way, although it seems so easy that it will be patched.
This requires the Ring of Life Protection, which can be found at the No Man's Wharf. This ring prevents loss of your Humanity and souls on death, but breaks afterwards. This ring can be repaired for 3000 at the blacksmith giving a constant 3000 Souls per Human transfer rate. A +1 Ring of Life Protection (Also prevents petrification) can be purchased from Vengarl in the Shaded Woods.
Best Answer
No, it doesn't affect the entire named area. It only affects the area between the bonfire on which the ascetic is used and the next bonfire. All enemies after the next bonfire will not be affected. For example, the first Aldia's keep bonfire will affect the rats outside the keep, the black phantom within the keep, the mirror knight enemies, the ogre and the giant basilisk but will not effect any enemies beyond that point as they all fall within the vicinity of the second bonfire, despite all the enemies beyond that point still belonging to Aldia's Keep. If you used an ascetic on the second bonfire, then all the aforementioned enemies would not be affected, and only the enemies between the second bonfire and the boss (including the boss, as the boss is 'associated' with the second bonfire) will be affected. I know it's a poor explanation, but hopefully it gave you an idea as to how the mechanic works.