OK. I've indexed a couple of sentences to it.

This sense isn't in the kokugos but it's very common (also used in the example sentence displayed on WWWJDIC).
I've changed my mind about the note I wrote; it wasn't clear. Probably better to have no note at all and instead use a different PoS tag. We "aux" on some similar entries. How this PoS should be used is still an open discussion on the mailing list, but I'll go with it for now.

@@ -18,0 +19 @@
+<pos>&aux;</pos>
@@ -20 +21 @@
-<s_inf>after neg. verb stem or adjective stem</s_inf>
+<gloss>if not ...</gloss>
@@ -22 +23,9 @@
-<gloss>if not ...</gloss>
+</sense>
+<sense>
+<pos>&exp;</pos>
+<pos>&aux;</pos>
+<xref type="see" seq="1632350">なければならない</xref>
+<misc>&abbr;</misc>
+<misc>&uk;</misc>
+<gloss>have to ...</gloss>
+<gloss>must ...</gloss>

I meant to add my thanks for working on it.

I've fixed the sentences.

Sentences for indexing:
1. 水がなければ、何者もこの地球上には生きられないだろう; パスポートがなければ、出国など論外だ
2. 急がなければ、学校に遅刻しますよ; タバコを吸わなければ、長生きできるだろう; 渋滞がひどくなければ大丈夫です; 忙しくなければ今週末に一緒に魚釣りに行きませんか

I think having "if it is not ..." on sense 1 is somewhat confusing. I understand the reasoning for doing it (having read the discussion below), but semantically, it belongs with the other sense.
I think it would be better to ignore the 無い/ない distinction, and instead generalise the sense 2 glosses so that they cover both verb and adjective use.

@@ -12 +11,0 @@
-<xref type="see" seq="1529520">無い・ない・1</xref>
@@ -14,3 +13,3 @@
-<gloss>if it does not exist</gloss>
-<gloss>if it is not there</gloss>
-<gloss>if it is not ...</gloss>
+<gloss>if (it) doesn't exist</gloss>
+<gloss>if there is no ...</gloss>
+<gloss>if (one) doesn't have ...</gloss>
@@ -19,2 +18 @@
-<pos>&suf;</pos>
-<xref type="see" seq="2257550">ない・1</xref>
+<pos>&exp;</pos>
@@ -22,2 +20,3 @@
-<gloss>unless one ...</gloss>
-<gloss>if one does not ...</gloss>
+<s_inf>after neg. verb stem or adjective stem</s_inf>
+<gloss>unless ...</gloss>
+<gloss>if not ...</gloss>