Mouse is very important to use a computer and nothing can completely replace it. If you lost your mouse then you can use your keyboard to control the mouse. Its not as quick and efficient as the mouse but still you can use it in many important situations. To do this go to control panel, Ease of Access, and select change how your keyboard works which comes under ease of access center.
To make it simple just type 'change how your keyboard works' in the start menu. From the first option select the setup mouse keys option and you can configure how to use the keyboard. Check the turn on mouse keys box and select the settings you need.
Try to choose like the image given. If you enable those settings you can enable or disable the controlling with keyboard option by turning on the number lock key. To move the mouse up down left and right use the numberpad 8,2,4 and 6 respectively. to left click the mouse select numberpad 5. 
You can use shift or control buttons to speed up the mouse if the box with this option is ticked. You can use this for anything