This is just a temporary arrangement for current season. We still do not know about what will happen next year or next season. Assuming there is a security threat in IPL 4 there will be some resistance from foreign players. The solution for that could be either worked out by choosing apprpriate venues or moving to a different (say like last year when matches were held in South Africa).
Assuming the matches are held in India itself with a few changes there will be non-participation from players in certain countries but if the organizers make alternate arrangements and convince them atleast majority will participate - its all a part of the Money Game. Who wants to miss this opportunity - probably a few from English speaking countries can afford to miss IPL for security reasons - because they have options to play elsewhere - for other countries there could be some diplomatic talks and finally they will agree to play unless there is some war like situation with Pakisthan or other neighbo