Economically thinking the return is very low right now from bidbot delegation. One can earn more with same SP by curating manually considering the low STEEM prices.
If there is no bidbot - my answer is (e) - some would sell votes manually (this is happening now) and self vote, some would power down and go away, many would delegate to projects and earn rewards. But less of those delegators would manually curate as it takes a lot of time.
I assumed that ROI wouldn't be great right now with delegation to bots, but likely still way ahead of anything else?
Curation can be automated, but the best results are still found front-running large bids on low valued posts :(
Leasing SP to others can earn slightly more ROI than bidbots but obviously differs bot to bot and lease to lease deals.
Yes, you are absolutely right. Only front-running large bids or large self-voters can earn huge curation. I am running a kinda ethical one, so can say it firsthand.