Yes they did.

Not only was CKS serious about retaking the mainland, he actively planned and trained troops for it, leveraging US and Japanese military advisor expertise, and lobbying for US support. Some operations were even put into motion.

For example, this article (PDF, English abstract on second page) published by Academia Historica, Taiwan's official custodian of national records, discusses how CKS organized the "Wuhan Project" to retake the mainland.

The article (Chinese) mentions facts such as on June 26, 1949, CKS spoke in a military meeting and said that they will eradicate the communists within 3 years. Chiang coined the slogan of "6 months training to reform our spirits; 1 year to attack to succeed in 3 years."

The next year, Chiang revised his slogan to, "1 year of preparations, 2 years to attack, 3 years to sweep clean and 5 years to success."

The article also cited Chiang's diary, showing that Chiang noted down two big possible opportunities for attack: (1) when WWIII starts. (2) when the communist party starts in-fighting. And that he needs to strengthen his troops to leverage those opportunities, even if they take 10 years.

From 1950 to 1956, Chiang closely supervised the army's planning for a landing attack on the south-eastern coast of China.

Then came the Wuhan Project of 1957-1961, when Chiang planned a paratrooper landing around Yunan to establish a base of operations for retaking the mainland. Troops trained heavily for this, and Chiang even considered spliting ways with the US because the US did not want to get involved in another full-out war so soon.

Part of the plan where he would connect with and support the remaining ROC guerillas staying around the China-Myanmar border were even put into motion, with US logistics support. Unfortunately one of the supply plane was shot down by Myanmar troops and the operation was exposed at the UN, forcing Chiang to back off.

Eventually, the failed Wuhan Project was aborbed into the more famous Project Glory that started in 1961.

So yes, not only did Chiang expect to return to the mainland, he actively planned and trained troops for it.