Yes - Although the "\" is not common in most user entered data (but common in Rich Text" which is less commonly used) my biggest concern with this code is the speed of the initial pos statement searching through a significant volume of text. (Although with disable bind only updated values are written). As you say if there is a lot of text and "\" and a lot of replacement, this could impair performance.
Considering this, it may be wise to have some service flag in the control to be able to turn this off when required for significant volume of write activity.
A point to note, is that the underlying microsoft string routines from C++ that PB may be relying on internally are notoriously slow compared to other functions - to the point that microsoft does not recommend them in high volume situations. There are various postings offering assembly replacements for such string handling. This is why I would wish for PowerBuilder to address this as an option which is managed by the datawindow - or even more helpful, to have SQL Anywhere give us the ability to turn it off as other vendors have.