How many endings does The Blood of Dawnwalker have?

Seven. Two are decided by which ally you finish the month beside, four by choices you make, and one by letting the thirty days elapse.

What happens if the thirty days run out?

You do not get a game over and you are not reloaded. Brencis's investiture proceeds, the sacrifice happens, and the story resolves into the ending called Time Runs Out.

Can one run reach every ending?

No. The ally-gated endings are mutually exclusive, so The Patricide and The Knyazmaker cannot both happen in a single run.

Endings

Seven endings, gated three different ways. Knowing which is which is enough to steer toward one without spoiling it.

Gated by: ally

Decided by who is standing beside you at the end of the month. These two are mutually exclusive.

The Patricide
Finish the month alongside Lacra.
The ending you reach by siding with Lacra, the vrakhir who came to kill Brencis.
The Knyazmaker
Finish the month alongside Crake and the rebellion.
Side with Crake, and the question stops being who dies and becomes who rules next.

Gated by: choice

Decided by what Coen does, rather than who he does it with.

The Turncoat
Turn on the people who were counting on you.
The ending for a Coen who takes the court's offer instead of the valley's.
The Folk Hero
Finish as the valley's own.
The ending where Vale Sangora keeps the story it wanted about you.
A Hero They Deserve
Leave the valley.
Walk out of Vale Sangora rather than settle it.
Together Forever
A dream ending.
The ending the game files under dream rather than under outcome.

Gated by: the clock

Decided by the thirtieth day arriving without you.

Time Runs Out
Let the thirtieth day pass.
Not a game over. The sacrifice happens, and the game keeps going into the ending that follows from it.

Gated by: ally

The Patricide

The Knyazmaker

Gated by: choice

The Turncoat

The Folk Hero

A Hero They Deserve

Together Forever

Gated by: the clock

Time Runs Out