The cave is too narrow to get around the slug, and the path behind you is sealed due to a cave-in. Your only option is to fight.

By its movement rate, you judge the slug will need 5 rounds before you will be cornered (You act before the slug in each round).

You have a shortsword and a bow with arrows, and begin the encounter with the shortsword equipped. The sword deals more damage, but the bow and arrows have better accuracy and defensiveness (until you are cornered). If you choose to use the bow, you must spend one round putting the sword away and drawing the bow. Switching back from the bow to the sword also requires a round. For the sake of argument, assume the cave is well-lit.

Assume that each round, the slug advances toward you, forcing you into the corner, no matter what else occurs that round. For the first 5 rounds, the slug can attempt to bite if you have attacked with the sword. It cannot attack if your move was firing with the bow or switching weapons. After the first 5 rounds, you are “cornered” and the slug can attempt to bite no matter what your action was for that round.

Here are the probabilities of the various attacks:

Shortsword
----------
Chance to hit while not cornered: 90%
Chance to hit while cornered: 90%
Damage on successful hit: 1d10 (1dm means you roll 1 m-sided die)

Bow
---
Chance to hit while not cornered: 100%
Chance to hit while cornered: 50%
Damage on successful hit: 1d6

Slug bite
---------
Chance to hit while not cornered & you attacked with sword: 50%
Cannot attack while not cornered if you switched weapons or fired bow: 0%
Chance to hit while cornered (regardless of your weapon/action): 90%
Damage on successful hit: 1d4

The slug begins the encounter with 20 hit points. You begin the encounter with 11 hit points. Assume death occurs immediately upon reaching 0 hit points (this applies to both you and the slug). If the slug dies, you survive and have succeeded, no matter how few hit points you may have left (even if it’s only 1). If you die, you have failed.

Here is an example of one scenario:

Standing: Slug has 20 hit points, I have 11

Round 1
Action: sword (90% chance to hit)
Result: hit
Damage: 7 (1d10)
Slug: bite (50% chance to hit)
Result: miss
Damage: N/A
Standing: Slug has 13, I have 11
We get one step closer to the corner.

Round 2:
Action: switch weapons
Result: N/A
Damage: N/A
Slug: N/A (cannot bite)
Result: N/A
Damage: N/A
Standing: Slug has 13, I have 11
We get one step closer to the corner.

Round 3:
Action: bow (100% chance to hit)
Result: hit
Damage: 2 (1d6)
Slug: N/A (cannot bite)
Result: N/A
Damage: N/A
Standing: Slug has 11, I have 11
We get one step closer to the corner.

Round 4:
Action: switch weapons
Result: N/A
Damage: N/A
Slug: N/A (cannot bite)
Result: N/A
Damage: N/A
Standing: Slug has 11, I have 11
We get one step closer to the corner.

Round 5:
Action: sword (90% chance to hit)
Result: hit
Damage: 4 (1d10)
Slug: bite (50% chance to hit)
Result: hit
Damage: 4 (1d4)
Standing: Slug has 7, I have 7
We get one step closer to the corner. I am now cornered.

Round 6:
Action: switch weapons
Result: N/A
Damage: N/A
Slug: bite (90% chance to hit)
Result: hit
Damage: 3 (1d4)
Standing: Slug has 7, I have 4

Round 7:
Action: bow (50% chance to hit)
Result: hit
Damage: 5 (1d6)
Slug: bite (90% chance to hit)
Result: hit
Damage: 2 (1d4)
Standing: Slug has 2, I have 2

Round 8:
Action: bow (50% chance to hit)
Result: hit
Damage: 4 (1d6)
The slug is now dead and I have succeeded.
Standing: Slug has 0, I have 2

A) What is the best strategy to maximize your chances of surviving regardless of how many hit points you might end up retaining, and how many hit points would you expect to have following such a strategy?
B) Suppose instead we measure your ending hit points minus the slug's ending hit points and label this D, and your goal is to devise a strategy that maximizes D. Just to be clear, if you survive with 2 hit points (as in the example above), D is 2; if the slug survives with 2 hit points, D is -2. How would your strategy differ from (A)?