Hi, you can have 2 different charts, set both charts in a container and use 'Show condition' to show/hide them.
The bar chart by year can have a condition like Count(Distinct Year)>1, and the combo chart by month Count(Distinct Year)=1.
The tricky part could be to show quarter sales in a chart by month, for this I think you will need a field QuarterSales wich summarizes in months 3, 6, 9 and 12 the sales of the other months of each quarter.