OK

I don't think this should be an entry, either. It's no different from 食べまへん except it's more common in the ngrams. あらへん and かまへん are different and worth keeping because you couldn't arrive at あらへん from ない, and かまへん is irregular (if it were regular, it'd be かまわへん)

有りまへん	400	1.0%
在りまへん	0	0.0%
ありまへん	38068	99.0%

No need for such xrefs.

@@ -5,0 +6 @@
+<ke_inf>&sK;</ke_inf>
@@ -8,0 +10 @@
+<ke_inf>&sK;</ke_inf>
@@ -15,2 +16,0 @@
-<xref type="see" seq="1296400">ある・1</xref>
-<xref type="see" seq="2222860">まへん</xref>

If it is to be, then let us do it all the way.
Still, I will make one final argument against it: compounds from which the meaning is easily deductible by the constituent morphemes and in which those morphemes themselves are discernable by the morphology of the word (no contractions, etc.) do not require their own entry and have little reason to be given one; under these circumstances, it would be the same as adding a dedicated entry for every verb with ない or ぬ or any other helper attached to them. Would that do any harm? No, but it is fundamentally superfluous.

In any case, should this be accepted, I will be conducting identical changes to あらへん and others of the previously given list as they too are missing the kanji and cross-references.

@@ -3,0 +4,6 @@
+<k_ele>
+<keb>有りまへん</keb>
+</k_ele>
+<k_ele>
+<keb>在りまへん</keb>
+</k_ele>
@@ -8,0 +15,2 @@
+<xref type="see" seq="1296400">ある・1</xref>
+<xref type="see" seq="2222860">まへん</xref>

ありまへん	38068
あらへん	97232
構へん	1224
かまへん	18392

I'm comfortable with it. Aligning with あらへん.

@@ -8,2 +8 @@
-<pos>&n;</pos>
-<misc>&joc;</misc>
+<pos>&exp;</pos>
@@ -11,2 +10,3 @@
-<gloss>to not exist</gloss>
-<gloss>to not be</gloss>
+<gloss>not</gloss>
+<gloss>nonexistent</gloss>
+<gloss>not being (there)</gloss>