So far as I can tell from the 30 June 2012 financials: season tickets made up 12.2% of gross revenues; gate receipts made up 6.5% of gross revenues; corporate hospitality boxes made up 4.8% of gross revenues; and other match day receipts made up 1.9% of gross revenue. That's an aggregate of 25.4% of gross revenue.
TV and media revenue made up 59.6% of gross revenue and commercial, catering, and sponsorship revenue made up 14.8% of gross revenue--an aggregate of 74.4%.
Realistically, there's only so much that a reduction in fan attendance is going to do.