Saija's Journal: How do you protect against job takers?

Actually i'm working as a support engineer in a manufacturing plant, here we make some security documents(cheques, bonuses, credit cards and the like), my job is support some legacy applications, develop new applications as needed by the staff of the plant or the customers, some basic hardware support and a mix of IT and Developing duties.
Approximately in a month my wife will give birth to our daughter and therefore i'll have my paternity license which summed with some old vacation period will left me almost one and a half month out of the work, I'm the only one doing the stuff i do and we need some replacement while i'm out, there have been a wide range of people who might could be brought to replace me: freshly graduated engineers, students of what we call here "intermediate careers", support engineers of the other manufacturing plant we have, which it is in another city in the country, and so on.
In the middle of this searching for my replace the bosses notice some auxiliary guy who is studying the same carrer i studied, this guy has showed some "hungry" to take my job and i don't want this kid to take my job and kick me out of here.
What could i possibly do given the bosses liked the idea of him be my replace and with this they just avoid the hassle of interview and contract some outside guy? How could i save my job while i'm out in my license?