Modeling question: revolver cap

Two things:

1. The simplest answer is you need an equity infusion by the amount of the revolver overdraw. You should limit the revolver draw at the capped amount unless you're modeling a refi. 
2. The more practical answer is it depends on why you're cash flow negative... depends how folks define levered free cash flow, but if you're including M&A spend here in your walk to cash flow available for debt service, then realistically what you're doing is increasing your leverage capacity. This is most relevant for modeling something like roll-ups, but typically in financing packages for highly acquisitive companies, you'll have a term loan (let's say at 6x on a $100m EBITDA company), a revolver commitment, and a delayed draw term loan (aka DDTL; lets say $200m). This functions similarly to a revolver from a commitment/fee/mechanic perspective, and the way it typically works is you can continue to draw on it up to the amount of the original leverage level... so as you buy down your multiple with acquired tuck-ins, (i.e. if you had $100m of EBITDA and acquire $20m of EBITDA through a number of tuck-ins) your leverage multiple may have moved from 6x to 5x... you can draw on the DDTL to get you back up to 6x (so $120m of the $200m commitment), and practically this is how many of these acquisitive platforms fund their tuck-ins. However, if you had acquired $40m of EBITDA instead of $20m, you max your DDTL draw at the $200m initial commitment and would need a refi/new commitment to be able to get back up to 6x leverage and continue funding your M&A without organic cash flow.

Realistically you'd need to raise equity (assuming you can't up-size the revolver) but as others said, it depends on the specifics of the excercise.