The comma without the 'and' would have been incorrect grammar. Here we have two independent clauses which could exist as lone sentences:
I already had a lead to look into. If need be, I could come back later.
(The comma after 'be' is proper usage, but the number of pauses you want in a sentence is up to you, as long as the meaning is clear.)
These two clauses are independent, so they could not be joined by a comma. These are two examples of incorrect comma placement:
I already had a lead to look into, if need be, I could come back later.
OR (without the comma after 'be')
I already had a lead to look into, if need be I could come back later.
They need a conjunction to stitch them together in order for it to be grammatically correct:
I already had a lead to look into, and if need be, I could come back later.
OR
I already had a lead to look into, and if need be I could come back later.
The comma without the 'and' would have been incorrect grammar. Here we have two independent clauses which could exist as lone sentences:
I already had a lead to look into. If need be, I could come back later.
(The comma after 'be' is proper usage, but the number of pauses you want in a sentence is up to you, as long as the meaning is clear.)
These two clauses are independent, so they could not be joined by a comma. These are two examples of incorrect comma placement:
I already had a lead to look into, if need be, I could come back later.
OR (without the comma after 'be')
I already had a lead to look into, if need be I could come back later.
They need a conjunction to stitch them together in order for it to be grammatically correct:
I already had a lead to look into, and if need be, I could come back later.
OR
I already had a lead to look into, and if need be I could come back later.