What will happen if a table I/O update fail?

Right now in my UBE, I do a Select/Fetch Next before I update a record in a table so three table I/O commands total, just to make sure that record exists first before update.  To increase performance and table I/O is expensive, I plan to cut down on the number of table I/O commands and just issue the table I/O update command so going from three commands to just one.

If it finds the record then it will update it. What will happen if it can't find the record?  Is it going to stop my UBE or it just ignores it and continue?  Will I be fine with just one table I/O command?