1999 Dodge Ram V8 Four Wheel Drive Automatic 120000 miles

I noticed everytime My gas got down to 1/4 tank, It was very hard to start.It would turn over, however, I needed to keep it reved up to about 2 rpm's for about a minuet in order for it to stay started..Im told it is a fuel pump/filter..However, The mechanic said that if I just kept my tank at atleast 1/2 tank of gas or more at all times, I probobly wouldnt run into this problum again..My question is, what happens if I dont put out the $800 bucks now to fix it, whats the worst that could happen??..Can it like go out comletely as Im driving down the road or something??..Excuse me for my incompetence, but Im a girl!!..Can someone please tell me if it would eventualy fail all together or is thier a chance the truck can just live w/ this problum??