Will manic episodes in bipolar disorder become more frequent and intense and severe as the disease progresses?

Bipolar: Possible, especially if untreated or complicated by physical illnesses or advanced age.

Probably so w/o Rx: Bipolar disorder is believed to exhibit a kindling phenomenon, where each untreated mood episode (it doesn't matter if it is manic or depressive) is likely to increase the probability that the next mood episode will occur with a shorter interval than the last one and will last longer. Again, this presumes no treatment.