If you run out of Ticks then you simply run out of Ticks... because somebody will come along and say "How can I have Timer1 count an HOUR or a DAY or a WEEK"?

Eventually you run out of capacity for the Registers for the Time period you wish to count. There is nothing you can directly do about that...

So the usual solution is to preset the Timer to count say 0.5 Seconds (which is within range), and when the period has elapsed you simply increment a BYTE. When that BYTE has incremented to 12 (for 12 x 0.5 Seconds = your desired 6 Seconds), zero the byte (for the next 6 Second timing period) and toggle your LED. So basically you are supplimenting Timer1 with another eight or sixteen bits, but those you have to increment yourself rather than have it done for you.