No, your car cannot only run on the engine. The "IMA" in your car stands for Integrated Motor Assist which means that if either one is at fault, your car will not work. Both the engine and battery work in unison to move the car. The battery is built to last around 200,000KMs and sometimes even more. What mileage is your odometer displaying?
If you suspect your hybrid battery is weak, it'll give an "IMA" and check engine light at the same time because the faulty battery will put strain on the engine causing it to overheat and work double time. Have the check lights scanned using a proper OBD-II scanner. Then and only then, go for a replacement. Its even better to have Honda Center have a look at it and then go for a replacement. Usually its just a battery terminal issue with most Civic hybrids/Insights.
You can buy a good condition used Civic/Insight hybrid battery for 60-70k with almost 80-90% life remaining on it. Your old battery will go for 5-8k. I know this because my friend just had the battery in his 2012 Insight replaced just a month ago.