The south can't and won't carry Biden if a competitor solidly accumulates momentum in the first states; especially if that momentum causes his southern support to falter. If he loses the first three and California, you may as well forget it.
It's possible he might right his currently sinking ship and recapture those states, but I would doubt it. It strikes me as being very unlikely, particularly after his miserable debate performance, where his competitors did well by contrast.
Right now, this is the primary schedule per wikipedia
February 3: Iowa caucuses
February 11: New Hampshire primary
February 22: Nevada caucuses
February 29: South Carolina primary
March 3: Super Tuesday (Alabama, Arkansas, California, Colorado, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Vermont, and Virginia primaries); American Samoa caucuses; Democrats Abroad party-run primary for expatriates features a March 3–10 voting period.
March 10: Idaho, Michigan, Mississippi, Missouri, and Washington primaries; North Dakota firehouse caucuses (identical to a party-run primary).
March 14: Northern Mariana Islands caucuses
March 17: Arizona, Florida, Illinois, and Ohio primaries
March 24: Georgia primary[310]
March 29: Puerto Rico primary[311]
April 4: Alaska, Hawaii, and Louisiana primaries; Wyoming caucuses
April 7: Wisconsin primary
April 28: Connecticut, Delaware, Maryland, New York, Pennsylvania, and Rhode Island primaries
May 2: Kansas primary; Guam caucuses
May 5: Indiana primary
May 12: Nebraska and West Virginia primaries
May 19: Kentucky and Oregon primaries
June 2: Montana, New Jersey, New Mexico, and South Dakota primaries
June 6: United States Virgin Islands caucuses
June 16: District of Columbia primary (bill proposing a move to June 2 has been approved by the DC Council and now only awaits final approval by the US Congress for enactment)[312][313]
My feeling is that by March 17 we will know if have a sure nominee of if it is still one big mess. If two or even three candidates win a number of states by then and nobody has a majority of delegates, it is going to be very very interesting.