I think it would depend significantly on the forward velocity of the aircraft at the time. Taking bird strikes as an analogy, the bird imparts a very high force to the blade over a short period of time. In engineering terms, we refer to this as an impulse. Roughly speaking impulse = average force * duration of interaction. The impulse is equal to the imparted momentum, where momentum = mass * velocity.
Assume the aircraft is in forward motion at the time of the impact, and assume the impact takes place near the tip of the fan blade. Then there would be two components of the impulse. A tangential component due to the rotational velocity of the blades, and an axial component due to the forward velocity of the aircraft.
Although I can't quantify it, I believe the tangential component would be relatively low. The metal leading edge of the blade acts as a fairly efficient knife and cuts through ingested objects without too much force. I've seen high speed videos of bird strike tests. The fan blades cut through the bird like a hot knife through butter. The blades just slice up the bird and keep on going as if nothing happened.
The axial component of the interaction though, is absorbed by the fan blades by the portion of the bird that hits them head on. This causes the blades to bend back, and if it is too large could cause them to break.
FAR 33.76 requires the engine manufacturer to test the ingestion of a large (8 lb / 3.65 kg) bird at a forward velocity of 200 knots.
So if a person of, say, 20 times larger mass (160 lb / 73 kg), was ingested near the beginning of the takeoff roll at a 20 times lower velocity of 10 knots, then since the total momentum is about the same, I think the result would be mostly the same as the results of a 33.76 bird ingestion. That is to say, no hazardous engine effects (i.e. no uncontained failures), although a loss of thrust might be experienced.
On the other hand, if a person of 20 times larger mass was ingested near takeoff rotate at a forward velocity of 130 - 160 knots, then the axial momentum would be an order of magnitude higher than the engine OEM tested during engine certification. There is no way to tell for sure what would happen in this case (at least not without contacting the OEM and asking them to analyze the situation with finite element models). However, failure of one or two fan blades is probably not unreasonable. I would expect that such a failure would be a contained failure though, as the 9X has passed the 33.94 blade containment test. For purposes of a fictional story, if you stretched it to three blades and said it was an uncontained failure, that would still be within the world of believability (but again, only if the impact occurs at high forward velocity)
